It is commonly seen that members of a species are largely alike. An elephant resembles other elephants, a rose plant
looks alike other rose plants, and children resemble their parents, even grandparents or great grandparents.
This resemblance among the individuals of a species has given rise to a general truth ‘like begets like’ which implies
continuity of life. It is, however, not absolutely true as the members of a species are seldom exactly alike. For instance,
in human beings, the children often have some individual characters in which they differ from one another,
and also from their parents. In fact, their differences are as marked as their resemblances.
This is true about other species as well.
The similarities and differences among the members of a species are not coincidental. They are received by the young ones from
their parents. The hereditary information, in fact, is present in the gametes (egg and sperm) which fuse to form the fertilized
egg or zygote during sexual reproduction. The zygote then develops into an organism of a particular type. For instance, fertilized
eggs of sparrows hatch into sparrows only and the fertilized eggs of pigeons hatch into pigeons only. Similarly, a cow gives birth
to calves only. The wheat plant gives rise to seeds which, in turn, develop into wheat plants.
Heredity :- The transmission of characters [or traits] from one generation to another generation.
OR
The transmission of characters from the parents to their offsprings.
Variations :- The differences in the characters [or traits] among the individuals of a species are called
variations. e.g. Plant height - Tall, dwarf & middle.
Ear lobe in human being :- The lowest part of our ear is called earlobe.
u In most of the people, the ear lobe is hanging and it is called free earlobe.
u In some people, the earlobe is closely attached to the side of the head and it is called attached ear lobe.
Heredity involves inheritance of basic body design (similarities) as well as subtle changes (variations) in it from one
generation to the next generation, i.e., from parents to the offspring. When individuals of this new generation reproduce,
the offsprings of second generation will have the basic body design, the differences that they inherit from first generation
as well as newly developed differences.
Asexual reproduction involves single parent. When a single individual reproduces asexually, the resultant two individuals
again after sometime reproduce to form four individuals. All these individuals would be similar.However, there would be
only very minor differences between them. These very minor differences arise due to small inaccuracies in DNA copying.
Sexual reproduction, on the other hand, generates even greater diversity. This is so because sexual reproduction involves
two parents (father and mother) and every offspring receives some characters of father and some characters of mother.
Since, different offsprings receive different combination of characters of their parents (father and mother), they show
distinct differences (variations) among themselves as well as from their parents.
The variations accumulate and pass on to more and more individuals with each generation.
(i) Chance separation of chromosomes during gamete formation (gametogenesis).
(ii) Crossing over during meiosis.
(iii) Chance coming together of chromosomes during fertilization.
(iv) Mutations, i.e., alterations in the genetic material.
All the variations in a species do not have equal chances of surviving in the environment in which they are generated.
Depending upon the nature of variations, different individuals would have different kinds of advantages. For instance,
bacteria that can withstand heat will survive better in a heat wave than the others. In other words, environmental
factors select the variants and this selection forms the basis of evolution.
Mendel was born on 22 July 1822 at Heinzendorf in Austria at Silesia village. Mendel was worked in
Augustinian Monastry as monk at Brun city, Austria.
In 1856-57, he started his historical experiments of heredity on pea(Pisum sativum) plant.
His experimental work continued on pea plant till 1865 (19th centuary).
The results of his experiments were published in the science journal. "Nature For Schender Varein" in 1866.
This journal was in Germen language. Title is ' Verschue Uber pflangen hybridan'.
This journal was published by 'Natural History society of Bruno'.
A paper of Mendel by the name of Experiment in plant Hybridization published in this journal.
Mendel were unable to got any popularity no one understand of him. he died in 1884 (due to kidney
disease (Bright disease)) without getting any credit of his work.
After 16 years of Mendel's death in 1900 Mendel's postulates was rediscovered.
Mendel experiment remain hidden for 34 years.
Rediscovery by three scientist independently.
1. Carl Correns - Germany - (Experiment on Maize)
2. Hugo deVries (Holland) (Experiment on Evening Primerose)
3. Erich von Tschermak Seysenegg - (Austria) (Experiment on different flowering plants)
A recognizable feature of human beings or any other organisms are called characters.
eg. (i) Height (ii) Complexion (iii) Shape of hair (iv) Colour of eyes (v) Shape of nose
Traits :- Various forms of a character are called traits.
S. No. Character Dominant Recessive
1. Length of Plant Tall Dwarf
2. Flower position Axial Terminal
3. Shape of pod Inflated Constricted
4. Colour of pod Green Yellow
5. Shape of seed Round Wrinkled
6. Colour of cotyledon Yellow Green
7. Colour of flower Violet White
1. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B
exists in 60% of the same population, which trait is likely to have arisen earlier?
2. How does the creation of variations in a species promote survival?
3. What is the role of DNA for bringing variation?
A breeding experiment dealing with a single character is called a monohybrid cross.
Mendel first selected ‘pure line’ plants (i.e., the plants that produced similar traits generation after generation).
He, then, cross pollinated such plants having the contrasting traits, considering one trait at a time. For instance,
in one such cross breeding experiment, he cross bred garden pea plant having round seeds with plant having wrinkled seeds.
In this monohybrid cross, the pollen grains from the flower of the desired plant raised from round seeds were transferred over
the previously emasculated flower of a plant raised from wrinkled seeds or vice-versa. After the transfer of pollen grains,
the cross pollinated flower was properly covered and seeds produced were allowed to mature. All the seeds of
F1 generation were carefully observed. Mendel observed that all the seeds of
F1 generation were of round type and there were no intermediate characteristics.
He raised plants from F1 seeds and allowed the flowers to self-pollinate to produce the seeds of F2 generation.
The flowers were kept covered from the beginning to avoid unwanted pollens to reach these flowers. In F2 generation,
Mendel observed the appearance of both round and wrinkled seeds in approximately 3 : 1 proportion.
Fig. 1 Monohybrid cross
1. The trait B has arisen earlier since it in 60% population while trait A is merely in 10% which is
newly arisen and not spread to large number.
2. Creation of variation may be suitable for a population to fight against some new change in
environment while those which do not have this variation will not be able to fight with such
changing conditions and will die.
3. DNA is the molecule which has heredity information stored in it, DNA can make its own copy by
replication but sometimes this replication brings errors, which shows variation in expression of
their respective characters.
A cross involving two pairs of contrasting characters.
or
A cross in which two pair of contrasting characters are studied at a time.
In one such cross, Mendel considered shape as well as colour of the seeds simultaneously. He selected pure line plants and
then cross pollinated flowers raised from seeds of round shape and yellow colour with those from wrinkled seeds and green colour.
Mendel observed that in F1 generation all seeds had the features of only one parental type, i.e., round shape and yellow colour.
He raised plants from F1 generation seeds and allowed the flowers to self pollinate to produce the seeds of F2 generation.
These flowers were kept covered from the beginning. In F2 generation, Mendel observed the appearance of four types of combinations.
These included two parental types (round shaped and yellow coloured seeds, and wrinkled shaped and green coloured seeds) and two
new combinations (round shape d and green coloured seeds, and wrinkled and yellow coloured seeds) in approximately same proportion.
Fig.2 Dihybrid cross
Dominant gene :- The gene which decided the appearance of an organism even in the presence of an alternative gene.
Recessive Gene :- The gene which can decide the appearance of an organism only in the presence of another identical gene.
Chromosomes :- A thread - like structure in the nucleus of a cell formed of DNA which carries the genes.
Genotype :- The genetic constitution of an organism.
or
The description of genes present in an organism e.g. TT, tt, Tt.
Phenotype :- External and morphological appearance of an organism for a particular character.
Allele :- Alternative forms of a gene which are located on same position [loci] on the homologous chromosome.
F1 Generation :- When two parents cross or breed to produce progeny [or offsprings],
then their progeny is called F1 generation or first filial generation.
or
The offspring produced by the parental generation.
F2 generation :- When the first generation progeny cross or breed among themselves to produce second progeny,
then this progeny is called second filial generation or F2 generation.
or
The offspring produced by the F1 generation
Hybrid :- A new form of plant resulting from a cross or breeding of different varieties of a plant is known as a hybrid.
Pure-breeding :- Characteristics that appear unchanged generation after generation.
Dominant characters :- Any character that appears in the F1 generation offspring from a cross between parents
possessing contrasting characters such as tallness & dwarfness in pea plants.
Recessive characters :- Any character present in the parental generation that does not appear in the F1
generation but reappears in the F2 generation.
Homozygous :- A condition in which the 2 members of an allelic pair are similar. e.g. TT, tt.
Heterozygous :- A condition in which the 2 members of an allelic pair are dissimilar. e.g. Tt.
Offspring :- Organisms produced as a result of sexual reproduction.
Homologous chromosomes :- All chromosomes found in pair & chromosomes of a pair are called homologous chromosomes.
Non-homologous chromosomes :- Chromosomes of different pair are called non-homologous chromosomes.
Genes :- Unit of heredity which transfers characters from parents to their offsprings during reproduction.
Gene ® Protein synthesis ® Enzymes [Controls phenotype of a character]
On the basis of Mendel's work, 3 basic laws of inheritance were proposed.
(i) Law of Dominance
(ii) Law of Segregation
(iii) Law of Independent Assortment
Law of dominance :- In crossing between organisms pure for contrasting characters of a pair, only one character of the
pair appears in the F1 generation. This character is termed dominant while the one which does not express itself in
F1 generation is termed recessive.
Law of segregation :- Allele or genes remain together and segregate at the time of gamete formation.
This means that the alleles don't mix in the hybrids [Non-mixing of alleles]
This is also known as the Law of Purity of Gametes.
Law of Independent Assortment :- This law states that - when individuals differing in 2 or more than 2 pairs of
contrasting characters are crossed, the inheritance of any one pair is not affected by the presence of the other.
e.g. The inheritance of tall character is not way related to the smooth character of the seed. Rather,
the 2 characters are inherited independent of each other.
Advantage of pisum sativum
Pisum sativum was a unique plant selected by Mendel for his experimentations had following importance-
How is the sex of newborn individual determined ? In human beings, the sex of the individual is largely genetically determined.
In other words, the genes inherited from our parents have assumed that similar gene sets are inherited from both parents.
If that is the case, how can genetic inheritance determine sex ?
All human beings these are 23 pairs of chromosomes are present out of these 23 pairs, are autosomes (similar in males and females)
and 1 pair is called sex chromosome (different in males and females). In males sex chromosome are XY and in females sex chromosome are XX.
Fig.3 Sex determination
So, it is clear from the above that male is responsible for producing male child.
l The term Genetics comes from "gene" word – means "to grow".
l The term "Genetics" coined by Bateson.
l Study of heredity and variations is called Genetics.
l Father of Genetics - Gregor Johann Mendel.
l Father of Modern Genetics - Bateson.
l Father of Experimental Genetics - Thomus Hunt Morgan.
l "Heredity" term coined by Spencer.
l Bateson coined terms Genetics, Allele, Homozygous, Heterozygous, F1 and F2 Generation.
The expanded form of DNA is deoxyribonucleic acid. It was first isolated by the scientist Frederick Meisher from the nucleus
of the pus cells in 1869. He named it as 'nuclein' or nucleic acid because of its acidic nature. Later, it was experimentally proved
by the scientists Griffith (1928), Avery, McLeod and McCarty (1944) that DNA is the carrier of the genetic information from
generation to generation. It transmits the hereditary characters in a coded language from parents to the offsprings
(i.e., from one generation to another).
DNA is a macromolecule or polymer. It is made of very large number of ‘nucleotide’ units and hence is termed polynucleotide.
Each nucleotide unit in a DNA molecule is made up of three components
1. Deoxyribose sugar :- It is a pentose sugar.
2. Nitrogenous base :- Each nucleotide unit has a nitrogen containing base. In a DNA molecule, nitrogenous bases are of two types :
(a) Purines :- The purines in a DNA molecule are — Adenine (A) and Guanine (G).
(b) Pyrimidines :- The pyrimidines in a DNA molecule are — Cytosine (C) and Thymine (T).
3. Phosphate group :- The phosphate group contains one phosphorus atom and four specifically linked oxygen atoms.
Thus, there are four types of nucleotides in a DNA molecule depending upon the kind of nitrogenous base present in each nucleotide.
Double Helical Model of DNA
J. D. Watson and F.H.C. Crick proposed the double helical model of DNA in 1953. They were awarded the Nobel Prize for this
discovery in 1962. The important features of the double helical model are
(i) DNA molecule is made up of two long polynucleotide strands forming a double helical structure (double helix) just like a
spiral staircase. Each helical turn of the DNA molecule is 3.4 nm in length in which ten nucleotide base pairs are present.
(ii) Deoxyribose sugar and phosphate molecules are joined alternately to form the backbone of each polynucleotide strand.
The nitrogenous base of each nucleotide is attached to the sugar molecule and projected towards the interior of the double helix.
(iii) In the interior of double helix, the nitrogenous bases of two polynucleotide strands form a pair with the help of hydrogen bonds.
Adenine (A) always pairs with thymine (T) and guanine (G) always pairs with cytosine (C).
Thus, the two polynucleotide strands of the DNA molecule are joined by hydrogen bonds between specific nitrogenous bases.
Such a specific pairing of the bases of the opposite strands of the DNA molecule is called complementary pairing. Adenine
(A) and thymine (T) are complementary to each other. Similarly, guanine (G) and cytosine (C) are complementary to each other.
The hydrogen bonding between the specific nitrogenous bases keeps the two strands to hold together. Therefore,
all the base pairs remain stacked between the two strands.
Four different types of blood groups in human beings are : A, B, O, AB
O ® universal donor
AB ® universal recepient
The term evolution has been derived from the Latin word 'evolvere' means unroll.
Evolution can be defined as sequence of gradual development of complex form of life from simple
form of life over the course of geological time " Descent with modification."
Evolution is of two types –
(i) Chemical evolution
(ii) Organic evolution.
After origin of a living cell the next questions that arose was how did so many different species of complex life form come into existence?
Here are various view points.
Carolus linnaeous :– Said that no species is new i.e. each species originates from pre existing species.
Jeans baptist lamarck :– Explained in his book namely philosoophie zoologique, the theory of inheritance
of acquired characters or lamarkism. This theory states that use and disuse of an organ leads to change in the organ.
Which is inherited by the offsprings. The favourable variations which remain for longer period of time results in evolution of new species.
This theory was discarded by August Weismann as he experimentally proved that even after cutting tails of mice for
21 generation tailless mice was never born.
Charles Robert Darwin was born on 12 Feb, 1809 in England. He travelled by HMS Beagle ship along with Dr.
Henslow. He visited many islands of south America, South Africa, Australia and Galapagos Islands.
Darwin was influenced by two books. "Principal of population" of malthus. "Principal of Geology of charls leyell.
Fig.4 
Fig.5
In his book origin of species he answered this questions. The theory presented by him is called theory of natural selection or Darwinism.
Alfred Russel wallace :– He travelled south eastern Asia and south America. The idea of natural selection striked in his mind
wallace wrote an essay and sent it to Darwin. On the tendency of varieties to depart indefinitely from original type.
There is striking similarity between the views of Darwin and Wallace.
Charles Darwin explained the mechanism of origin of new species by natural selection. But he failed to explain the mechanism
of source of heritable variations. This was explained by Hugo de Vries a dutch botanist. According to him, heritable variations
arise when there is a change in genes of the germplasm (protoplasm of germcell). He called it mutation.
Life originated on earth through chemosynthesis or formation and coming together of biochemicals.
It is called naturalistic theory or theory of chemical origin of life. The theory was given by Russian scientist
Oparin (1924) and British turned Indian scientist J.B.S. Haldane (1929).
(i) At the time of formation of earth lighter elements present on the surface were in their atomic state, viz, hydrogen, carbon, nitrogen and oxygen.
(ii) With the slight lowering of surface temperature of earth, the lighter elements interacted and formed water (H2O), methane (CH4),
ammonia (NH3), molecular hydrogen (H2) and carbon dioxide (CO2). They formed a reducing hot atmosphere of earth. It was exposed to
ultraviolet radiations, cosmic rays, lightning and hot lava from volcanoes. Methane, ammonia, hydrogen and other molecules interacted and
formed sugars, amino acids, alcohols, fatty acids, nucleotides and other biochemicals.
With further interactions and polymerisation, complex organic molecules were formed. Their aggregation formed coacervates or colloidal
complexes that developed covering membrane and nucleic acids to produce protocells or primitive cells.
Experimental Proof : Stanley Lloyd Miller and Harold C. Urey (1953) assembled an apparatus to provide conditions similar to those of early earth.
They took a mixture of ammonia, methane and hydrogen (2 : 2 : 1) and water, and exposed it to electric sparks, heating and cooling to resemble
lightning and provide temperature from 800ºC to just below 100ºC. After one week, 15% of carbon from methane had been converted into
organic compounds of sugars, organic acids, amino acids, purines and pyrimidines. The first primitive organism would arise from further chemical synthesis.
Fig.6
Variations are the structural, functional or behavioral changes from the normal characters developed in living organisms.
There is an inbuild tendency to variation during reproduction. Both because of errors in DNA copying as a result of sexual reproduction.
Variations provide raw materials for evolution. These may be inheritable or non inheritable, only inheritable variation participate in evolution.
Type of variation :– On the basis of nature of cells where variations occur variations are of two types.
(i) Somatogenic variations or Acquired traits (ii) Germinal (Blastogenic) variations.
An Illustration :– Consider the following example.
1. A group of twelve red beetles living in bushes with green leaves.
2. Beetles in the population can generate variations because these are reproducing sexually.
3. Crow can eat the beetles. The more beetles the crow eat, the fewer beetles are left for reproduction.
Fig.7
Fig.8 Variation in a population inherited and otherwise
Now consider the following situations :–
The reason why organisms resemble their parents lie in the precise copying of their genes.
Which carry hereditary characters from one generation to the next. On the other hand no two
off springs have exactly the same genes. This is because offspring of sexually reproducing organisms
receive varying combination of genetic material from both parents such variation result from mutations
(errors in DNA copying). Variations also result from genetic recombination during sexual reproduction.
The random changes in the gene frequency occurring by chance alone. The effect of genetic drift is very
small in large population and large in small populations.
Biological species concept : A species is a sexually interbreeding group of individuals separated from other species by
the absence of genetic exchange. Members of species are capable of breeding with one another and produce living,
fertile off spring but are unable to breed with members of other species normally.
Gene pool : Sum of all the genes of all the members of a species.
Speciation occurs when the gene pool of a population is some how reproductively isolated from other sister population
of the parent species and gene flow no longer occurs between them. Then a population splits into independent species.
Which become reproductively isolated from each other.
On basis of period taken in speciation there are two types of mechanism of speciation.
The process of formation of one or more new species from an existing species is called speciation.
Let us try to understand this concept by taking the example of beetles.
* Large population of beetles occur on a mountain range.
* Few beetles started feeding in neighborhood.
* Gene flow continued in two places.
* They may get isolated at larger distance because of existence of river.
* Gene flow decreases and finally stops.
* Two sub populations change with time because of genetic drifts and natural selection.
* Later they became reproductively isolated.
* Two new species came up.
* This can occur as a result of change in chromosome number.
* Micro evolution is very important this mean that the changes may be small but significant.
Speciation due to inbreeding, genetic drift and natural selection will be applicable to all sexually reproducing
animals geographical isolation does not play any role in the speciation of a sexually reproducing animals
and self pollinating plants.
Classification : Classification is the system of arrangement of organism in certain groups or subgroups on
the basis of hierarchies of certain characteristics.
The characteristics are the details of appearance from structure, function and behaviour Phylogenetic taxonomy
is branch of classification on the basis of evolutionary relationship on the basis of common ancestry.
Studies on similarities in structure of different organisms suggests that present forms have evolved through
a process of slow and gradual change called evolution. They include the following :
1. Homologous organs : Homologous organs are those structures which are different in appearance and
perform different functions but have similar basic structure and developmental origin.
This relationship is called homology.
Seal Bird Bat Horse Man
Appearance Flippers Wings Patagia Elongated
Thumb opposability Swimming flying Support, flying Running Grasping function
Fig.9
2. Analogous : Those organs which have different origin and structural plan but appear similar and perform similar
functions are called analogous organs. While this relationship is called convergent evolution or analogy.
eg : Wing of an insect and a bird, Hand of man & Trunk of elephant.
Fig.10
Analogy in these organs is due to similar adaptations to perform similar functions rather than their common ancestry.
3. Vestigial organs : Those organs which no longer have a function are called vestigial organs. These organs have reduced
structurally as well as functionally. It appears that these organs were once well developed and functional in ancestors
and later on due to their less use they became reduced.
eg : Vermiform appendix, ear muscles, third eyelid in man are reduced and function less.
Fig.11
Common ancestry and inter-relationship :
Various organisms are inter connected their resemblance suggest a common ancestry.
Eg : Heart of Fish ® Only two chambers
Heart of Amphibia ® Three chambers
Heart of Reptilia ® Three chambers and half
Heart of Bird and mammals ® Four chambered
Fig.12
Connecting links : Some living organism have characteristics of two groups. They are known as connecting links.
Eg : Lung fish - show connection between fishes and amphibians.
Fig.13
Various connecting links
(i) Virus - Between living and non living
(ii) Euglena - Between plants and animals
(iii) Proterospongia - Between protozoa and porifera
(iv) Neopilina - Between annelida and mollusca
(v) Peripatus - Between annelida and arthropoda
(vi) Archaeopteryx - Between reptiles and birds
(vii) Balanoglossus - Between non chordates and chordates
(viii) Chimera - Between cartilaginous fish and bony fish
(ix) Lung fish - Between fishes and amphibia
(x) Platypus - Between reptiles and mammals
(xi) Echidina - Between reptiles and mammals
Jurassic period is known as golden age of reptiles.
Dinosaur of dromaesaur family had feather on body and fore limb.
Huxley called birds as glorified reptiles.
Carnivorous dinosaur called velociraptor had a wish bone like birds.
Evidences from embryology :
A comparative study of the stages of embryonic development of animals reveals that in their early stages they were very similar.
These embryonic stages reflect thus ancestry. The embryological
stages of an organism give us an idea about the stages of its
evolution. For example when we study the human embryo, we find
that at a certain stage it has gills. This suggests that fish is one of the earliest ancestors in the evolution of mammals including
human beings.
Fig.14
1. Fossils : Fossil is an organic relic of a long dead life form.
Or
Fossils are the petrified remains and for impressions of the hard parts of the extinct organism preserved in
the sedimentary rock or other media.
Palaeontology : Study of fossils is known as palaeontology.
Fig.15 
Fig.16
How do fossils form layer by layer ?
Let us start 100 million years ago. Some invertebrates on the seabed die, and are buried in the sand. More sand accumulates,
and sandstone forms under pressure.
Millions of years later, dinosaurs living in the area die, and their bodies, too. are buried in mud.
This mud is also compressed into rock, above the rock containing the earlier invertebrate fossils.
Again millions of years later, the bodies of horse-like creatures dying in the area are fossilized in rocks above these earlier rocks.
Much later. erosion by, sun, water flow, wears away some of the rock and exposes the horselike fossils.
As we dig deeper, we will find older and older fossils.
Living fossils : The animals which underwent little change during long geological periods.
Important living fossils
1. Peripatus, Limulus (Arthropoda)
2. Nautilus, Neopilina (Mollusca)
3. Lingula (Brachiopoda)
4. Latimeria (Coelacanth fish)
5. Sphenodon (Reptilia)
Determination of the age of fossil : There are three ways of determining age of the fossils.
1. Relative method : If we dig into the earth and starts finding fossils it is reasonable to suppose that the fossils
we find closer to the surface are more recent than the fossils we find in deeper layer.
2. Using Radioactive Elements : The age of a fossil is determined with the help of certain radioactive elements
such as uranium present in the rock.
3. Carbon dating : Carbon dioxide of air contains a small proportion of radioactive carbon (C14).
CO2 is used during photosynthesis and there is equal proportion of C14 among carbon atoms of all organisms.
The radioactivity of C14 is lost at a precise rate half life of C14 is about 5,600 years.
If a fossil shows radioactivity one fourth of that found in the living organisms the organisms died about 11,200 years ago. (Two half lives.)
Evolution by stages
Evolutionary changes are fundamental characteristics
of living organisms such changes may be convergent. It means that the similar looking structures may have different ancestral designs.
This can be explained by example of eye.
Eye : Eyes of insects, octopus and vertebrates have similar looks but different structures and must have separate evolutionary origin or different
ancestral designs. Rudimentary eye can be useful to some extent.
Fig.17
Fig.18 Examples of convergent evolution
Feathers : The function of feathers was insulation in cold weather later this feature might have proved to be useful for the purpose of flight.
Dinosaurs is example depicting presence of feathers in them but these were not used for flying later birds seem to have adaptation of flying
using feathers. This shows close relationship of birds to reptiles and proves that characters appearing as an variation can be useful
later to perform different functions.
Cabbage : Humans have developed different types of vegetables from the wild cabbage by artificial selection.
S.No. Vegetable evolved Edible part
1. Cabbage Selection for fleshy terminal buds and short distance between the leaves.
2. Brussel's sprouts Selection for fleshy lateral buds.
3. Kohl rabi Selection for fleshy stem.
4. Kale Selection for large sized leaves so it is a leafy vegetable.
5. Broccoli Selection for leafy sized and arrested flower development.
6. Cauliflower Selection for fleshy sterile flower.
Fig.19 Evolution of wild cabbage [Divergent evolution]
Molecular phylogeny
Ancestors of different organism including humans can be traced by studying the change in their DNA.
A change in DNA means a change in its protein sequences. The ancestry or phylogeny determined by comparative
study of DNA sequences is called molecular phylogeny.
Studies in molecular phylogeny help in the classification of organisms.
Haeckel propounded 'The theory of recapitulation or 'Biogenetic law'. Which states that an individual organism in its
development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny means ontogeny repeats phylogeny.
Though organic evolution involves descent with modification in which there is a progressive trend of emergence of more or
more complex body designs from earlier similar body designs by gradual changes but evolution should not be equated
with progress because of following reasons.
1. In evolution older species are not eliminated during formation of new species and most of older and simple species still survive.
eg : Earliest organisms like bacteria are found even in many hospitable habitats like hot springs,
deep-sea, thermal vents, Antarctic ice. etc.
2. The evolved species are not always better than the parental species evolution depends upon natural selection and genetic
drift which is together result in population which is reproductively isolated from the parental species.
Evolutionary history of man has been built from the palaeontology (fossil studies) and molecular biology (especially DNA changes).
For example :- It is not true that human beings have evolved from chimpanzees. Rather both human beings and chimpanzees have
common ancestors a long time ago. That common ancestors is likely to have been neither human or chimpanzee.
The two resultant species have probably evolved in their separate ways to give rise to the current forms.
Anthropology : the scientific study of tracing of human evolution is called anthropology.
Scientists involved in studying human evolution are called anthropologists.
Studies have revealed that human evolution started in Africa and earliest human type was
Australopithecus Africans. African ape man fossil was discovered by Prof. Raymond Dart fossil of skull of
5-6 years old baby from old Pliocene rock of Tuang region (S.Africa). He name it Tuang baby. It had many ape
like characters but had a bipedal locomotion like man. The cradle of human evolution is East Africa where genetic
foot prints of earliest members of human spec ies Homosapiens can be traced. A couple of hundred thousand years
ago some of own ancestors left across the planet from Africa.
Fig.20 Human evolution
The first human types, evolved into modern man Homosapiens through a number of intermediate human types.
Fig.21 Homo erectus erectus ® Java man
Fig.22 Homo erectus pekinesis ® Peking man
Fig.23 Homo sapiens neaderthalensis ® Neanderthal man
Fig.24 Homo sapiens fossils ® Cro-magnon man
In the course of their evolution these migrant human types went forward and backwards and moved in and out of south Africa.
Modern man evolved from Cro-Magnon man about 25000 years ago and spread all over the world about 10,000 years.
Negroid : African Pygmies and bushman
Caucasian : Italian English
Eastern : Chinese Japanese Eskimos
Mangolid : These ethnic group differ from one another in their skin colouration lips and hair pattern but all of these
belong to same species because these are not reproductively isolated from one another. All human races have same
chromosomes number and similar grass morphology of chromosomes.
Fig.25 Human evolution
Man of future :
Homo sapiens futuralis.
(A prediction by American anthropologist Dr. Sapiro.)
Q.1 If a trait 'N exists in10% of a population of an asexually reproducing species and a trait B exists in
60% of the same population, which trait is likely to have arisen earlier?
Ans. Trait B is likely to have arisen earlier than trait A, because in asexual reproduction! there is lesser chances of creation of variations.
New traits are developed due to small inaccuracies produced during DNA copying. These new traits will be in very small proportion
of population as compared to already existing traits. Therefore, trait B, which exists in 60% of population must have arisen earlier
than the trait A that occurs in 10% of the population.
Q.2 How does the creation ofvariations ina species promote survival?
Ans. Variations in a species is caused due to error in DNA copying during reproduction. All the variations do not have survival value,
only some of them can be beneficial iiI. certain environmental conditions. These are called pre-adaptations. These variations help
the individuals of a species to survive in the harsh environmental conditions. These useful variations are selected by nature and are
the cause of evolution. The individuals with useful variations then increase in numbers through differential reproduction in the populations.
For example, in heat waves, most of the bacteria will die but a few which have preadaptation or variations to tolerate heat will survive and reproduce.
Q.3 How do Mendel's experiments show Lhat traits may be dominant orrecessive?
Ans. Mendel crossed two varieties of garden pea plant having contrasting visible characters. He He considered one pairof
contrasting characters, for example, height (tall and dwarf).
The cross between the two, i.e., pure tall plant with pure dwarf plant resulted in production of only tall plants in F1 generation.
When F1 plants were self-pollinated, Mendel observed both tall and dwarf plants in F2 generation in a pproxiamtely 3:1 ratio.
The trait of dwarfness which was not expressed in F1 generation, is called a recessive trait. The trait of tallness which expresses
itself in the presence of its contrasting character is termed as dominant trait.
Q.4 How do Mendel's experiments show that traits are inherited independently?
Ans. Independent inheritance of traits were proved by dihybrid crosses. In dihybrid cross, Mendel considered two pairs of contrasting
characters. In the F1 generation, both the dominant traits appeared. Self breeding of F1 yielded four types of individuals in F2
generation and the ratio was 9 : 3 : 3 : 1.
For example: When a tall plant with round seeds (TTRR) is crossed with short plants having wrinkled seeds (ttrr).
The plants of F1 generation were all tall with rounded seeds (TtRr). It indicates that the characteristics of tallness and roundness
of seeds were dominant. Self breeding of F1 plants, yielded 9 tall round seeded, 3 tall wrinkled seeded, 3 short round seeded and 1
short wrinkled seeded plants. Tall wrinkled seeded and short round seeded plants are new combination which can develop if the
trait are inherited independently. If the two traits are taken individually, F2 ratio would be same as for monohybrid crosses (3 : 1),
i.e., 12 tall, 4 short, 12 rounded seeds, 4 wrinkled seeds.
Q.5 A man with blood group A marries a woman with blood group 0 and their daughter has blood group O.
Is this information enough to tell you which of the traits -blood group A or 0 -is dominant? Why or why not?
Ans. No, the information is not enough to tell us which trait of blood group A (IA) or blood group O (I°) is dominant because each
individual carries two alleles of a gene and recessive trait appear only when both the alleles are similar. There may be two possibilities:
(i) Blood group A is dominant and blood group O is recessive: Daughter can have blood gr up 'O' only when both the recessive alleles occur
together as in mother (IOIO) and father has one allele of A and other of 'O' blood group(IA IO).
(ii) Blood group 'O' is dominant and blood group ‘A’ is recessive: In t:his situation, father should carry both alleles of A (IAIA) while the
mother may be homozygous (IOIO) or heterozygous (IOIA).
The daughter will have one dominant allele of O (IOIA).
As both the possibilities can occur, the given information is unable to tell whether allele for blood group A or O is dominant.
Q.6 How is the sexofthe child determined inhumanbeings?
Ans. The sex of a child in human beings is determined by the type of gametes contributed by male during fertilisation.
Human males (44 + XY) form two types of sperms, androsperms (22 + Y) and gynosperms (22 + X). Both are formed
in equal numbe.r It is a chance whether an androsperm or gynosperm fuses with the egg. If the male gamete with X
chromosome fertilises the ovum (X), the sex of the child will be female (XX). However, if male gamete having Y
chromosome fertilises the ovum (X), the sex of the child will be male (XY).
Q.7 What are the different ways in which individuals with a particular trait may increase in a population?
Ans. There are various ways in which individuals with a particular traitmay increase innumber. For example,
(a) Survival value (Natural selection): TI e trait which is selected by nature has survival value over the others.
Through differential reproduction, it increases in population. For example, green colour beetles increased in number
as they were not easily located by crows in the green bushes because of their colour.
(b) Genetic Drift: Accident may cause decline in a particular population. The survivor with certain other combinations
of traits will increase in number in population. The traits may not give any extra benefit to population.
(c) Abundance of food: Availability of food for the organisms also determines their number.
Q.8 Why are traits acquired duringthe lifetime of an individual not inherited?
Ans. Acquired traits are notinherited because they are acquired during the lifetime of individuals. These traits do not bring
any change in the DNA or germ cell of the individual. These characters induce changes in the non-reproductive tissues
(somatic cells) only and not in the germ cells. Tne alterations (variatjons) in DNA is passed through germ cells to the
next generations. For example, in his experiment Weismanrl (1892) cut the tails of mice for 21 generations buta tail
still developed in the 22nd generation.
Q.9 Why are the small numbers of survivingtigers a cause of worry fromthe pointofview of genetics?
Ans. A small number of surviving tigers is a cause of worry because a small population is always at a risk of extinction
due to the following reasons:
(i) The possibility of lesser recombinations and variations which are essential for maintaining vitality and vigour of the species.
(ii) Decreased adaptability towards the environmental changes
(iii) Increased threat to survival due to habitat destruction and poaching
(iv) Excessi ve inbreeding that may cause inbreeding depression
Q.10 What factors could lead to the rise of a newspecies?
Ans. The factors which could lead to the formation of new species are:
(i) accumulation of variations in a population (ii) natural selection
(iii) reproductive isolation (iv) genetic drift (v) absence of gene flow.
Q.11 Willgeographical isolation be a major factor in the speciation of a self-pollinating plant species? Why or why not?
Ans. No, geographical barriers will not be a major factor in the speciation of self-pollinating plant species because there is no gene flow
among members of the species. Self-pollination occurs within a palnt and is not affected by any type of isolation. Slef-pollinated
plants like pea or wheat can accumulate variations due to mutation and other factors and form new species.
Q.12 Will geographical isolation be a major factor in the speciation of an organism that reproduces asexually? Why or why not?
Ans. Geographical isolation will notbe a major factor in speciation because recombination of genes is absent in asexual reproduction.
In asexual reproduction, single parent is involved and a physical barrier can separate two differernt organisms. So, variations
arising in them do not get diluted but spread to all subsequent generations. Geographical isolation helps in speciation due to
formation of separate gene pool and has no role in speciation of asexually reproducing organisms.
Q.13 Give an example of characteristics being used to determine how dose two species are in evolutionary terms.
Ans. The closeness of two species is determined by the presence of some similar characteristics. For example, thorns of Bougainvillea
plant and tendrils of Passiflora plant have same basic structural design (modified branches) but perform different functions
(homologous organs). They have evolved from a common ancestor having fundamental structural design but have developed
into thorns and tendrils subsequently and perform differernt functions.
Q.14 Can the wing ofa butterfly and thewing of a bat be consideredhomologous organs? Why or why not?
Ans. No, wings of a butterfly and wings of a bat cannot be considered as homologous organs because both of them are fundamentally
different in their origin and structure. The wings of a butterfly are integumentary outgrowths with hollow tubes whereas wings of
a bat are modified forelimbs ocvered with skin. The organs which have a different origin and structure but similar in function are
called analogous organs.
Q.15 What are fossils? What do they tell us about the process of evolution?
Ans. Fossils are the remains or impressions of dead animals and plants that existed earlier. They are often termed as written documents
of evolution because they directly indicate the presence of types of flora and fauna in different geological ages. Study of fossils
indicate the gradual complexity of organisms. Fossils tell us the following about the process of evolution:
(i) Fossils provide direct evidences to support organic evolution.
(ii) They indicate the evolutionary stages in the life of an organism/organ.
(iii) Fossils also help in tracing the evolutionary rela tionshi p among different organisms.
Q.16 Why are human beings who look so different from each other in tenns of size, colour and looks belong to the samespecies?
Ans. Human beings belong to the same species despite of differences in size, colour and looks because they share
same gene pool and can reproduce among themselves to produce fertile offspring. Differenrces in size, colour and looks are based on
predominance of specific alleles and their interaction with environment.
Q.17 Inevolutionary terms, can we say which among bacteria, spiders, fish and chimpanzees have a ‘better’ body design? Why or why not?
Ans. In evolutionary terms, better body design refers to one which is complex, elaborate and given an extra competitive edge over other organisms.
Out of bacteria, spider, fish and chhllpanzee, has a more elaborate body design and organisation. But all the organisms have a specific body
design which is selected to survive in their respective habitat. So, in terms of that, all these four organisms have a good body design which
suits their surrounding environment and helps them in their survival.
Q.18 A study found that children with light-coloured eyes are likely to have parents with light-coloured eyes. On this basis,
can we say anything about whether the light eye colour trait is dominant or recessive? Why or why not?
Ans. No, we cannot say with certainty whether light eye colour is dominant or recessive. However, the probability is that light eye colour is
recessive because both children and their parents have light coloured eyes. A recessive character always appears only when an individual
contains both the recessive alleles. If the parent has a dominant trait, the children also have that trait in dominance. Had the light eye
been a dominant trait, the recessive dark eye colour might have appeared in some of the children due to chance of segregation.
Q.19 How are the two areas of study, evolution and classification, interlinked?
Ans. Classification is the process of grouping the organisms on the basis of some similarities and differernces.
These similarities can be morphological (external) or anatomical (internal), which will define their evolutionary relationships.
Their differernces explain different adaptations and divergence from common ancestor. In this way evolution and classification are interlinked.
Q.20 Explain the terms analogous and homologous orans with examples.
Ans. Refer to text.
Q.21 Outline a project which aims to find the dominant coatcolourindogs.
Ans. (i) Survey the dog populationin a locality and find out differentcoat coloursindogs.
(ii) Observe the lineage where coat colour of parent and offspring are same since there is possibility of
having same alleles or a gene in these lineage.
(iii) Allow crossing between two such lineage with different coat colours.
(iv) Observe F1 generation for coat colour. It is probably the dominant coat colour which appears.
(v) Cross the F1 progeny to get the ratio in F2 generation.
Q.22 Explain the importance of fossils in decidingevolutionary relationships.
Ans. Fossils are remains and impressions of organisms that lived in remote past. The strata-wise arrangement of fossils will indicate the
occurrence of different forms of life at differeny times. It is found that earlier fossils generally belong to simple organisms and
complexity and elaboration of characters increase gradually with evolution. Fossils are direct evidences in support of organic
evolution and help in determining evolutionary relationships between organisms. They indicate how one group has evolved
from another.
Q.23 What evidence do wehave for the origin of life from inanimate matter?
Ans. Miller and Urey supported the origin of life from inanimate matters. They assembled an apparatus which had a spark chamber
to producelightening, a boiling flask and a condenser. They introduced a mixture of CH4, NH3, H2 and H2O (water vapour) into
this apparatus. The gaseous mixture was exposed to electric discharge, boiling (800°C) and condensation with the temperature kept
just below 100°C. This experiment continued for few days. At the end of a week, 15% of carbon from methane has converted into
simple organic compounds of amino acids, sugars, organic acids and nitrogenous bases. The experiment clearly proved that organic
compounds (building blocks of life) developed from inanimate matter in the remote past whenthehot earth was cooling and they
took partin origin of life on earth.
Q.24 Explainhow sexual reproduction gives rise to more viable variations than asexual reproduction.
How does this affect the evolutionof those organisms thatreproduce sexually?
Ans. Variations arise during sexual reproduction due to:
(i) Chances of separationofhomologous chromosomes a t the time of gametogenesis .
(ii) Crossing over between the chromosomes
(iii) Chance of coming together of chromosomes at the time of fertilisation
(iv) Genetic mutation atthe time of DNA replicatio.
In asexually reproducing organisms, only mutation takes place. Thus, in asexually reproducing organisms, rate of appearance
of variations is quite low as compared to sexually reproducing organisms. The variation of sexually reproducing organisms are
more viable than varJables o fasexually reproducing organisms. The reason of variations is reshuffling of genes that do not ocah·
in asexually reproducing organisms. Here most of the changes are harmful and show negative impact on evolution.
Due to the abundance and viability of variations, the rate of evolution in sexually reproducing organisms is high.
Q.25 How is the equal genetic contributionofmale and female parents ensured in the progeny?
Ans. During sexual reproduction, genetic materials of two parents combine together to form a new individual.
Both male and female parents contribute 50% of genetic material each. Thus, the offspring will have half of the
information of [ather and half of the mother. Therefore, both parents contribute equal genetic material to the
offspring through formation and fusion of gametes.
Q.26 Only variations that confer an advantage to an individual organism will survive in a population.
Do you agree with this statement? Why or why not?
Ans. No, because variations in an individual arises due to many reasons such as natural selection, genetic drift, mutation, etc.
They may not be beneficial for the organisms but still they persist in the population. Only the lathal or extremely harmful
variations are eliminated, rest of them exist in a population.
1. Genetics is the branch of science which deals with the study of :-
(A) cell function
(B) cell structure
(C) heredity and variation
(D) relation between plant and environment
2. The term 'genetics' was coined by :-
(A) William Bateson
(B) Gregor Mendel
(C) Thomas Hunt Morgan
(D) W. Johannsen
3. The term 'gene' was introduced by :-
(A) Mendel
(B) Bateson
(C) Morgan
(D) Johannsen
4. When a gene exists in more than one form, the different forms are termed :-
(A) alleles
(B) heterozygotes
(C) genotypes
(D) complementary genes
5. The contrasting pairs of factors in Mendelian crosses are called :-
(A) alloloci
(B) paramorphs
(C) allelomorphs
(D) multiple alleles
6. Alleles of a gene are found on :-
(A) same chromosome
(B) any chromosomes
(C) homologous chromosomes
(D) nonhomologous chromosomes
7. Which statement about alleles is not true :-
(A) There may be several at a locus
(B) One may be dominant over another
(C) They may show incomplete dominance
(D) They occupy different loci on the same chromosome
8. An organism which receives identical alleles of a particular gene from both parents is :-
(A) homozygote
(B) hemizygote
(C) homothallic
(D) heterozygote
9. The genetic complement of an organism is known as :-
(A) genotype
(B) physiotype
(C) phenotype
(D) morphotype
10. The physical appearance of an individual is known as :-
(A) heterotype
(B) genotype
(C) morphotype
(D) Phenotype
11. The terms 'genotype' and 'phenotype' were introduced by :-
(A) Bateson
(B) Darwin
(C) Johannsen
(D) Mendel
12. What was Mendel's most important contribution to the
modern understanding of biology :-
(A) The concept of meiosis
(B) The concept of chromosome
(C) The concept that genes are ordered along chromosomes
(D) The concept that hereditary information comes in discrete units
13. Gregor Mendel was born in :-
(A) Austria
(B) Russia
(C) Czechoslovakia
(D) United Kingdom
1 4. Mendelism is related with :-
(A) Heredity in living beings
(B) Meiosis during sexual reproduction
(C) Mutations in living organisms
(D) None of the above
15. Mendel published the results of his experiments in the year :-
(A) 1568
(B) 1773
(C) 1866
(D) 1921
1. The life arose from nonliving molecules was suggested by ...........................
2. Experimental evidence in favour of chemical origin of life was provided by .................... and ..................
3. The process by which new species arise is called ...........................
4. The biogenetic law was proposed by ...........................
5. The fossils of birds ........................... show that birds have evolved from reptiles.
6. Darwin made an extensive study of the flora and fauna of the........................... Islands in South America.
7. The origin of species was written by ...........................
1. C 2. A 3. D 4. A 5. C 6. C 7. D
8. A 9. A 10. D 11. C 12. D 13. A 14. A
15. C
1. Anaximander 2. A.I. Oparin, J.B.S. Haldane 3. Speciation
4. Haeckel 5. Archaeopteryx 6. Galapagoes islands
7. Charles Robert Darwin
1. What is a gene ?
2. Write the scientific term used for 'science of heredity and variation'.
3. Define inheritance.
4. What term did Mendel use for what we now call the genes ?
5. How does the creation of variations in a species promote survival ?
6. Name the plant on which Mendel performed his experiments.
7. Define Variation.
8. What are the carriers of factors or genes ?
9. Name two human traits which show variation.
10. Write down five inherited 'characters' or traits.
1. Why did Mendel choose pea plants for his experiment ?
2. What is Mendel's genetics ?
3. If a trait A exists in 10% of a population of an asexually reproducing species and a trait B exists in 60% of
the same population, which trait is likely to have arisen earlier ?
4. A Mendelian experiment consists in breeding tall pea plants bearing violet flowers with short pea plants
bearing white flowers. The progeny all bore violet flowers, but almost half of them are short.
This suggests that the genetic makeup of the tall parent can be depicted as :-
(i) TTWW (ii) TTww (iii) TtWW (iv) TtWw
5. Explain the mechanism of sex determination in human beings.
1. Explain diagramatically a Mendel's dihybrid cross.
2. Briefly explain contributions of Mendel in Genetics.
· Fill in the blanks
1. The ratio phenotypic for the monohybrid cross is __________________.
2. Characters that are expressed in any conditions are called _________________ and characters that are expressed only in homozygous conditions are called _____________.
3. _________________ is physical and chemical expression of a character.
4. Every organism have ___________ sets of all genes, one inherited from ________________.
5. The formation of new species is known as ________________ basis of heredity.
6. Genes are _________________________________.
7. ____________ are preserved traces of living organism.
8. Classification of a species is infact a relation of their __________________.
· Multiple choice question with one correct answers
1. Genetics is the study of
(A) Inheritance
(B) Cell structure
(C) Only plants
(D) Only animals
2. If two parents have the genotypes AA × aa, the probability
of having an aa genotype in the F1, generation is
(A) 25 percent
(B) 50 percent
(C) 75 percent
(D) None of these
3. Sex-linked disorders such as colour blindness and hemophilia are
(A) caused by gene on the X-chromosome
(B) caused by gene on the autosome
(C) caused by gene on the Y-chromosome
(D) Expressed only in men
4. Your arm is homologous with
(A) a seal flipper
(B) an octopus tentacle
(C) a bird wing
(D) both (A) & (C)
5. Which option represents test cross
(A) TT × TT
(B) Tt × tt
(C) Both (A) & (B)
(D) None
· Assertion & Reason
Instructions: In the following questions as Assertion (A) is given followed by a Reason
(R). Mark your responses from the following options.
(A) Both Assertion and Reason are true and Reason is the correct explanation of ‘Assertion’
(B) Both Assertion and Reason are true and Reason is not the correct explanation of ‘Assertion’
(C) Assertion is true but Reason is false
(D) Assertion is false but Reason is true
1. Assertion: Chemical basis of heridity is DNA.
Reason: Cellular DNA is the information source for making protein in the cell.
2. Assertion: Genes are functional segment DNA.
Reason: Genes are responsible for the expression of an enzyme.
3. Assertion: Variation are formed during reproduction.
Reason: Errors in DNA copying and sexual reproduction do not causes evolution.
4. Assertion: Speciation is the phenomenon by which new spp. comes into existence.
Reason: Genetic drift does not lead to speciation.
5. Assertion: The birds have pneumatic or hollow bones with air sacs
Reason: These adaptations help them during flight
· Match the following (one to one)
Column-I and column-II contains four entries each. Entries of column-I are to be matched with
some entries of column-II. Only One entries of column-I may have the matching with the same
entries of column-II and one entry of column-II Only one matching with entries of column-I
1. Column I Column II
(A) Minor differences in progeny (P) Theory of evolution
(B) Gregor Mendel (Q) Transmission of characters from parents to child
(C) Heridity (R) Genetic drift
(D) Change in frequency of gene (S) Due to inaccuracies in copying of DNA
(E) Charles Darwin (T) Law of inheritance
2. Column I Column II
(A) Monohybrid cross (P) Wings of Bat and Bird
(B) Sex-chromosomes (Q) Not neccesary better then old
(C) Artificial selection (R) One pair (xx/XY)
(D) Analogous organ (S) production of different varities of cabbage from wild cabbage
(E) New species formed (T) 3 : 1
· Multiple choice question with one correct answers
1. Mendel formulated some laws which are known as
(A) Law of germplasm
(B) Law of origin of species
(C) Law of speciation
(D) Law of inheritance
2. Term ‘gene’ was given by
(A) Mendel
(B) Morgan
(C) Bateson
(D) Boveri
3. Mendel choose pea plants because
(A) They were cheap
(B) They were having seven pairs of contrasting characters
(C) They were attractive
(D) Of great economic importance
4. The resemblance of individual to their progenitors is due to
(A) Heredity
(B) Genetics
(C) Evolution
(D) None of these
5. Linkage is contradicton to_________law of Mendel
(A) Mutation
(B) Independent assortment
(C) Dominance
(D) Crossing over
6. Law of purity of gametes is also known as
(A) Law of inheritance
(B) Law of variation
(C) Law of independent assortment
(D) Law of segregation
7. Mendel formulated the law of purity of gametes on the basis of
(A) Dihybrid cross
(B) Monohybrid cross
(C) Back cross
(D) Test cross
8. A white flowered mirabilis plants rr was crossed with red coloured RR,
if 120 plants are produced in F2 generation. The result would be
(A) 90 uniformly red and 30 white
(B) 90 Non-uniformly coloured and 30 white
(C) 60 Non-uniformly coloured and 60 white
(D) All coloured and 40 white
· Multiple choice question with one or more than one correct answers
1. Mendel law’s of inheritance include
(A) Law of Dominance
(B) Law of segregation
(C) Law of independent assortment
(D) Law of variation
2. Human originated in Africa and migrated to
(A) Philippines
(B) India
(C) Indonesia
(D) Bering land bridge
3. Which of the following is originated from wild cabbage?
(A) Broccoli
(B) Kale
(C) Kohlrabi
(D) Brasicca
Genetics is the branch of biology that deals with heridity and variations and heridity is the ability of a living organism
to pass on its characters to its offspring. The transmission of dissimilar character is called variation.
In asexual reproduction only very minor differences between progeny are seen, due to small inacuracies in DNA
copying where as great diversity is generated in case of sexual reproduction variations afferts the survival of an organism.
Depending on the nature of variation, different individual would have different kinds of advantages.
1. Branch of biology deals with heredity & variations –
(A) Genetics
(B) Cell biology
(C) Zoology
(D) Palaeontology
2. Transmission of dissimilar character.
(A) Heredity
(B) progeny
(C) variation
(D) None of these
3. Great diversity is generated in case of
(A) Asexual reproduction
(B) sexual reproduction
(C) both (A) & (B)
(D) None of these
Gregor Johann Mendel (1822-1884) known as the father of Genetics. mendel was educated in a monastery and went on
to study science and mathematics at the university of vienna. After the failure in examination for a teaching certificate,
he came back to his monastery and started his experiments on garden pea. Mendel used a number of contrasting visible
cahracters of garden pea – round/wrinkled seeds, tall/short plant, white/voilet flowers and so on. After his studies on
garden pea he gave the law of inheritance.
Mendel gave three laws – law of Dominanc, law of segregation, law of independent assortment.
1. Mendel is known as ____________________.
2. On which plant Mendel worked?
3. How many law did Mendel gave?
4. In which examination did Mendel failed?
· Match the following (one to many)
Column-I and column-II contains four entries each. Entries of column-I are to be matched with some entries of column-II.
One or more than one entries of column-I may have the matching with the some entries of
column-II and one entry of column-II may have one or more than one matching with entries of column-I
1. Column I Column II
(A) Phenotypic ratio (P) 1 : 2 : 1
(B) Genotypic ratio (Q) 3 : 1
(C) Monohybrid cross/ratio (R) 9 : 3 : 3 : 1
(D) Dihybrid cross ratio (S) Tt × tt
1. Mendel conducted his hybridisation experiment with :-
(A) Chick pea
(B) Pigeon pea
(C) Garden pea
(D) Wild pea
2. Mendel studied seven contrasting characters for his breeding experiment
with Pisum sativum, which of the following character did he not use :-
(A) Pod colour
(B) Pod shape
(C) Leaf shape
(D) Plant height
3. The main reason of Mendel's successs in discovering the principles of inheritance was :-
(A) He considered each character separately
(B) He was lucky not to encounter linkage problem
(C) The plant was pure breeding
(D) All the above
4. Mendel was lucky in the choice of the material of his experiments, among the following,
which contributed, to his success ?
(A) He observed distinct inherited traits
(B) He qualitatively analysed his date
(C) He liked pea plants
(D) He considered only one character at one time
5. The year 1990 AD is highly significant for genetics due to :-
(A) Principle of linkage
(B) Chromosome theory of heredity
(C) Rediscovery of Mendelism
(D) Discovery of genes
6. Genotype means :-
(A) Genetic composition of the individual
(B) Genetic composition of the germ cell
(C) Genetic composition of plastids
(D) Genetic compositon of an organ
7. The physical manifestation of an organism's genes is its :-
(A) Environment
(B) Phenotype
(C) Genetic code
(D) Genotype
8. An organism with two identical alleles of a gene in a cell is called :-
(A) Homozygous
(B) Domainant
(C) Heterozygous
(D) Hybrid
9. When an individual is having both the alleles of contrasting characters it is said to be :-
(A) Heterozygous
(B) Dioecious
(C) Monoecious
(D) Linked genes
10. When an allele fails to express itself in F1 generation in the presence of other allele,
the former is said to be :-
(A) Recessive
(B) Codominant
(C) Complementary
(D) Epistatic
11. Alleles are :-
(A) Homologous chromosome
(B) Chromosome that have crossed over
(C) Alternate forms of gene
(D) Linked genes
12. Mendel's laws apply only when :-
(A) F1 in monohybrid cross shows two types of individuals
(B) The character are linked
(C) Parents are pure breeding
(D) First pair of contrasting character is dependent upon other pairs
13. Which of Mendel's procedures differed from those of his predecessor and
contributed most of his success ?
(A) He observed many characteristics of each trait
(B) He observed distinct inherited traits
(C) He quantitatively analysed his data
(D) He kept breeding records
14. If a plant is heterozygous for tallness, the F2 generation has both tall
and dwarf plants. This proves the principle of :-
(A) dominance
(B) segregation
(C) independent assortment
(D) incomplete dominance
15. Mendel crossed a pure white flowered recessive pea plant with a dominant pure red flowered plant.
The first generation of hybrids from the cross should show :-
(A) 50% white flowers and 50% red flowers
(B) all red flowered plants
(C) 75% red flowered and 25% red flowered plants
(D) all white flowered plants
16. If a couple has three daughters, what are the chances that the fourth child will be a son ?
(A) 100%
(B) 75%
(C) 50%
(D) 0%
17. If a heterozygous tall plant is crossed with a homozygous dwarf plant,
the proportion of dwarf progeny will :-
(A) 50%
(B) 75%
(C) 100%
(D) 25%
18. The crossing of a homozygous tall plant with a dwarf would yield F2 plants in the ratio of :-
(A) two tall and two dwarf
(B) one homozygous tall, one homozygous dwarf and two heterozygous tall
(C) all homozygous dwarf
(D) all homozygous tall
19. When a true breeding tall plant is crossed with a true breeding short plant and the F1 produced
is self pollinated to produce F2 ratio of true breeding tall and true breeding short plant in F2 will be :-
(A) 1 : 2
(B) 1 : 1
(C) 2 : 1
(D) 1 : 3
20. Blue eye colour in human is recessive to brown eye colour. The expected children of a marriage between
blue-eyed woman and brown-eyed male who had a blue-eyed mother are likely to be :-
(A) all blue-eyed
(B) three blue-eyed and one brown-eyed
(C) all brown-eyed
(D) one blue-eyed and one brown-eyed
21. The genotype of a dominant parent is determined by crossing it with
the recessive parent. This cross is called :-
(A) back cross
(B) test cross
(C) long cross
(D) out cross
22. The results of a test cross reveal that all the offspring resemble the
parent being tested. This parent must be :-
(A) heterozygous
(B) homozygous
(C) recessive
(D) haploid
23. Chromosome theory of heredity was postulated by :-
(A) Charles Darwin
(B) Gregor Mendel
(C) Sutton and Boveri
(D) Har Gobind Khorana
24. Which chromosome set is found in male grass-hopper ?
(A) XY
(B) X
(C) YY
(D) XX
25. Allosomes are :-
(A) bead like structures
(B) on chromosomes
(C) sex chromosomes
(D) rounded bodies
26. Escherichia coli is widely used in genetics research because it is :-
(A) easy to procure
(B) easily manipulated
(C) easy to handle
(D) easy to culture in laboratory
27. Mutation is :-
(A) a change that is inherited
(B) a change, which affects the parents only but never, inherited
(C) a change, which affects the offspring of F2 generation only
(D) a factor responsible for plant growth
28. Recessive mutation are expressed normally in :-
(A) has to express always since it is a mutation
(B) heterozygous condition
(C) neither in homozygous nor in heterozygous condition
(D) homozygous condition
29. The reason why some mutations, which are harmful,
do not eliminated from gene pool is that :-
(A) they are recessive and carried by heterozygous individuals
(B) they are dominant and show up more frequently
(C) genetic drift occur because of a small population
(D) they have future survival value
30. Mutations are usually induced by :-
(A) gamma rays
(B) alpha rays
(C) beta rays
(D) visible light
31. The plant that was made popular by "De Vries mutation theory" :-
(A) Triticum vulgare
(B) Oenothera lamarkiana
(C) Pisum sativum
(D) Primula vulgaris
32. Gene mutation is caused :-
(A) due to reproduction
(B) due to changes in the sequence of nitrogen bases
(C) due to linkage
(D) due to changes in the sequence of genes in DNA
33. Sex chromosomes may be found in :-
(A) unisexual plant
(B) unisexual flower
(C) monocarpic plant
(D) intersexual plant
34. Which one of the following is a sex-linked characteristic ?
(A) White eye in Drosophila
(B) Duffy blood group in human beings
(C) AB blood group in human beings
(D) Vestigial wing
35. Human offspring would be female, if 23rd pair of chromosome in zygote is :-
(A) YY
(B) XY
(C) XX
(D) XYY
36. "Barr body" is derived from :-
(A) autosomes in males
(B) autosomes in females
(C) X-chromosome in female
(D) X-chromosome in males
37. Down's syndrome is due to :-
(A) nondisjunction of chromosomes
(B) crossing over between genes
(C) linkage of genes
(D) sex linked inheritance
38. The DNA is the genetic material was proved conclusively by :-
(A) J D Watson
(B) Hershey and Chase
(C) Alfred Griffith
(D) Boveri and Sutton
39. Nobel Prize for "one gene one enzyme theory" was given to :-
(A) Beadle and Tatum
(B) Schleiden and Schwann
(C) Watson and Crick
(D) H Harris
40. Retrovirus has the following as its genetic material :-
(A) single stranded DNA
(B) double stranded duplex DNA
(C) DNA-RNA hybrid
(D) RNA
41. Of the following, which sequence is present in Rous Sarcoma Virus ?
(A) DNA ® RNA ® proteins
(B) DNA ® DNA ® proteins
(C) RNA ® DNA ® proteins
(D) RNA ® DNA ® RNA ® proteins
42. The term genome is used for :-
(A) diploid set of chromosomes
(B) polyploid set of chromosomes
(C) triploid set of chromosomes
(D) haploid set of chromosomes
43. The first successfully cloned mammal that gained world-wide publicity was :-
(A) Molly, a sheep
(B) Polly, a sheep
(C) Chance ; a bull
(D) Dolly, a sheep
44. The transgenic animals are those that have :-
(A) foreign DNA in some of its cells
(B) foreign DNA in all its cells
(C) foreign RNA in all its cells
(D) both (A) and (C)
45. The first hormone artificially produced by culturing bacteria is :-
(A) Insulin
(B) Thyroxine
(C) Testosterone
(D) Adrenalin