This Powerpoint Presentation is on the chapter Heredity and Evolution from class 10 Biology in CBSE Board. The contents of the presentation are from the NCERT science textbook for class 10 and Lakhmir Singh Biology Handbook Class 10.

1. -Chapter 9
- Biology

2.  A recognizable feature of a human being ( or any other organism) like
height, complexion, shape of nose and chin, colour of eye and hair etc
are called characters or traits.
 The transmission of traits from the parents to their offspring is called
heredity.
 The hereditary information is present in the gametes of the parents.
Thus, gametes constitute the link between one generation and the next,
and pass on the maternal and paternal characters or traits to the
offspring.

3.  The differences in the characters (or traits) among the individuals of a species is called
variation.
 The offspring is never a true copy of the parent.
 There are many kinds of variations in human species like:-
 Free and attached earlobes.
Different complexions ( Dark, Light brown, Dusky, Wheatish, Fair etc.)
Different eye colour ( Brown, Hazel, Blue, Green, Grey, Amber etc.)
Height ( tall or short)
 Chin (cleft or pointed)
 Hair colour ( Black, Brown, Blonde, Red, Golden etc.)
 Hair type ( curly, wavy, Straight etc.)
 Nose ( Snub, Thin, Pointed etc.)
Hazel eye colour Blue eye colour
Blonde Hair
Brown Hair

4.  The significance of a variation shows up only if it continues
to be inherited by the offspring for several generations.
 The great advantage of variation to a species is that it
increases the chances of its survival in a changing
environment.

5.  Chromosome : It is a thread-like structure in the nucleus of a cell formed of DNA which
carries the genes.
 Gene : It is a unit of DNA on chromosome which governs the synthesis of one protein that
controls a specific characteristic of an organism. Genes are actually units of heredity which
transfer characteristics from parents to their offsprings during reproduction.
 Dominant Gene : The gene which decides the appearance of an organism even in the
presence of an alternative contrasting gene is known as a dominant gene. It is represented by a
capital letter.
 Recessive gene : The gene which can decide the appearance of an organism only in the
presence of another identical gene is called a recessive gene. It is represented by the
corresponding small letter.
 Genotype : It is the description of genes present in an organism.
 Phenotype : It is the characteristic which is visible in an organism .
 First Filial Generation or F1 Generation : When two parents cross to produce offsprings, their
offspring is called First Filial generation or F1 generation.
 Second Filial Generation or F2 Generation : When the first generation offsprings cross among
themselves to produce second generation offsprings, then this offspring is called Second Filial
Generation or F2 Generation.

6. Gregor Mendel was the first scientist to make a systematic study of
patterns of inheritance which involved the transfer of characteristics
from parents to progeny.
Mendel chose pea plants for studying inheritance because pea plants
had a number of clear cut differences which were easy to tell apart. For
ex : tall and dwarf pea plants. Some pea plants produced round yellow
seeds while others produced wrinkled green seeds etc.
Another reason for choosing pea plants was that they were self
pollinating. Also, Mendel chose pea plants because many generations of
pea plants can be produced in a comparatively short time span and their
study is much simpler than that of animals.

7. Mendel's first law of inheritance or the Law of Segregation : The
characteristics (or trait) of an organism are determined by internal
“factors” which occur in pairs. Only one such factor can be present in a
single gamete.

8. Mendel’s second law of inheritance or Law of Independent Assortment states that In the
inheritance of more than one pair of traits in a cross simultaneously, the factors responsible for
each pair of traits are distributed independently to the gametes.

9. The characteristics or traits of parents are transmitted to their offsprings through genes
present on their chromosomes during the process of sexual reproduction.
Genes work in pairs. For every trait there is a pair of genes ( one dominant and one recessive).
Each parent passes only one of the two genes of the pair for each characteristic.
Though the offspring inherits two genes for each trait from its parents but the trait shown by
the offspring depends on which inherited gene is dominant of the two.

10.  When a male gamete fuses with a female gamete during fertilization,
they make a new cell called zygote with a full set of genes (on a full set
of chromosomes) . This zygote grows & develops to form a new
organism having characteristics (or traits) from both the parents which it
has inherited through genes.
 The two genes (or pair of genes) responsible for a particular
characteristics are always present on the corresponding positions of the
pair of chromosomes .

11.  A person has one of the four blood groups: A, B, O, AB.
 A and B are co-dominant genes whereas O is a recessive gene.
 The genes for blood groups are denoted by: IA ( A in superscript), IB etc.
 If the genotype is IA IA or IA IO, then the blood group is A.
 If the genotype is IB IB or IB IO, then the blood group is B.
If the genotype is IO IO, then the blood group is O.

12. The process by which the sex of a person is determined
is called sex determination .
 The chromosomes which determine the sex of a person
are called sex chromosomes .
 Sex chromosome in male is ‘XY’ and in female it is ‘XX’
If a sperm carrying ‘X’ chromosome fertilizes an ovum
then the child born will be a girl .
If a sperm carrying ‘Y’ chromosome fertilizes an ovum
then the child born will be a boy .
It is the sperm which determines the sex of a child .

13.  A trait of an organism which is not inherited but develops in response to the environment is
called an acquired trait.
 Acquired traits cannot be passed on to the future generations.
 Ex: Knowledge of doing something or any characteristic which was caused due to
environmental factors and not present by birth .
 A trait of an organism which is caused by a change in its DNA or genes is called an inherited
trait.
 These are characteristics which we receive from our parents.
 Only these traits can be transmitted to future generations.
 Ex: Eye colour, skin complexion etc.

14. 1. The epidermal cell of a plant contains 28
chromosomes. How many chromosomes are there in
each gamete produced by the plant?
2. A pure tall pea plant (TT) is crossed with a pure dwarf
plant (tt). What is the ratio of pure tall plants to pure
short plants in the F2 generation?
3. What are the visible characters in an organism known
as?
4. Which of the following is an inherited traits?
eye color, scarred face, skin complexion, hair texture,
size of body.
5. What are the phenotypes of the following types of
hybrid pea seeds.
(a) Rryy (b) rrYy (c) RrYy (d) RRyy

15. 1. 14 chromosomes
2. 1:1
3. Phenotype
4. Eye color is an inherited trait.
Scarred face is not an inherited trait
Skin complexion is an acquired trait, but environmental
factors can also affect skin complexion of a person.
Hair texture is an inherited trait, but it can be altered
manually.
Size of body is not an inherited trait.
5. (a) Round Green
(b) Wrinkled Yellow
(c) Round Yellow
(d) Round Green

16. Evolution is the sequence of gradual changes which take place in the primitive organisms over
millions of years in which new species are produced.
The more characteristics a species have in common, the more closely they will be related.
Some important sources which provide evidence for evolution are Homologous, Analogous,
Vestigial organs and fossils.
Archaeopteryx which is believed to be the
missing link between dinosaurs and birds.

17. Homologous organ : Organs which have same fundamental
structures but different in functions. Ex: wings of birds , hands of
humans.

18. Analogous organs : Organs which similar functions but different in their
structure. Ex: wings of insects and wings of birds

19. Vestigial organs : Organs which are nonfunctional in the present day
forms but were functional in ancestors. Ex: appendix, wisdom tooth
.

20. The remains of dead animals or plants that lived in the remote past are known as Fossils.
Fossils are obtained by digging into the Earth. The age of fossils are estimated by the relative
method or carbon dating method.
There are various kinds of fossils. Some important fossils are ammonite, trilobite and dinosaur.

21. Darwin’s theory can be described as follows:
 Within any population, there is natural variation. Some individuals have more favorable
variations than others.
 Even though all species produce a large number of offsprings, populations remain fairly
constant naturally.
 This is due to the struggle between members of the same species and different species for
food, space and mate.
 The struggle for survival within populations eliminates the unfit individuals. The fit individuals
possessing favorable variations survive and reproduce. This is called natural selection. The
individuals having favorable variations pass on these variations to their progeny from generation
to generation.
 These variations when accumulated over a long period of time, lead to the origin of new
species.

22. Natural selection is the process of evolution of a species whereby characteristics which help
individual organisms to survive and reproduce are passed on to their offsprings, and those
characteristics which do not help are not passed on.
Though Darwin’s theory was widely accepted, but it was criticized on the ground that it could
not explain ‘how the variations arise’. With the progress in genetics, the source of variation was
explained to be the Genes. Genes vary in natural population. Genetic variation is the raw
material of evolution. So, Darwin’s theory was modified accordingly. These days, the most
accepted theory of evolution is the Synthetic theory of evolution. In which the origin of species
is based on both ‘genetic variation’ and ‘natural selection’ .

24. A species is a population of organisms consisting of similar individuals which can breed
together and produce fertile offspring.
The process by which new species develop from existing species is known as speciation.
Important factors which could lead to formation of new species are:
 Geographical isolation of a population which leads to reproductive isolation due to which
there is no flow of genes between separated groups of population.
 Genetic drift due to drastic changes in the frequencies of particular genes by chance alone.
 Variations caused in individuals due to natural selection.

25. The eye is a complicated organ which cannot be generated by a single DNA change.
The complex body organs of animals such as eyes have been created in stages over many
generations.
First of all the basic eye like that of a flatworm which are simple eyespots which can detect light.
After this, more and more complex eyes were evolved in many organisms.
The structure of eyes in each organism is different.
The evolution of eye is an example of evolution by stages.

26. Sometimes an evolutionary change produced in an organism for one purpose later on becomes
more useful for an entirely different function.
For ex: Birds evolved feathers as a means of providing insulation to their bodies in cold weather
but later on these feathers became more useful for the purpose of flying. Even some dinosaurs
had feathers though they could not fly using feathers. Birds, however adapted feathers for
flying. The presence of feathers on birds tell us that birds are closely related to dinosaurs.

27. Different looking organisms can be created from the same basic design of the ancestors.
This is called Evolution by artificial selection.
For ex: Cabbage, broccoli, cauliflower, kohlrabi and kale can be made artificially from wild
cabbage.
When farmers wanted very short distances between the leaves of wild cabbage, the common
variety of cabbage was evolved.
When farmers wanted arrested flower development of wild cabbage, broccoli was evolved.
When farmers wanted sterile flowers of wild cabbage, cauliflower was evolved.
When farmers wanted swollen parts of wild cabbage, kohlrabi was evolved.
When farmers wanted to grow large leaves of wild cabbage, kale was evolved.

28. There is no real progress in the concept of evolution. Evolution is just the production of diversity
of life forms and shaping of this diversity by environmental selection. The only progress in
evolution is that more and more complex organisms have emerged over ages.
It is a common belief that chimpanzees are the ancestors of human beings. This is not true.
Actually, both chimpanzees and human beings had a common ancestor long time ago.

29. Human evolution has been studied using various tools of tracing evolutionary relationships like
excavating, carbon-dating, studying fossils and determining DNA sequences.
All human beings are a single species called Homo Sapiens.
It has now been established by research that the earliest members of the human species came
from Africa. So, irrespective of where we have lived for past thousand years, we all have African
roots.

30. Darwin’s theory of evolution tells us how life evolved from simple to more complex forms and
Mendel’s experiments give us the mechanism for the inheritance of traits from one generation
to the next. But neither tells us anything about how life began on earth in the first place.

31. 1. Which variety of cabbage evolved due to the
farmers opting for swollen parts of wild cabbage?
2. What is the science of heredity known as?
3. What is the scientific names of humans?
4. State one characteristic which shows tat birds are
closely related to dinosaurs.
5. Name the animal which was the link between
reptiles and birds.
6. Did human beings evolve from chimpanzees ? Why /
Why not ?
7. Name one way how the age of fossils are estimated.

32. 1. Kohlrabi.
2. Genetics
3. Homo sapiens
4. Some dinosaurs had feathers though they could not fly using
these feathers. The presence of feathers on birds tell us that the
birds are closely related to dinosaurs.
5. Archaeopteryx
6. Human beings have not evolved from chimpanzees. Actually,
both human beings and chimpanzees had a common ancestor a
long time ago.
7. Carbon-dating method or Relative method.