it is based on class 10 ncert science textbook

4. • It means the transmission of features/
characters/ traits from one generation to the
next generation.

5. 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.

6. 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.

11. • The transmission of characters [or traits] from
one generation to another generation.

13. 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 Blue eye
Blonde
Hair
Brown
Hair

21. 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:
Availability of detectable contrasting of several characters
Short life span of the plant
Normally allows self- fertilization but cross- fertilization can
also be carried out.
Large no. of seeds produced.
Mendel’s experiment – Mendel conducted a series of
experiments in which he passed the pollinated plants to study
one character( at a time).

22. Character Dominant Recessive
Length of plant Tall Dwarf(short)
Flower Position Axial Terminal
Shape of Pod Inflated Constricted
Colour of Pod Green Yellow
Shape of seed Round Wrinkled
Colour of cotyledon Yellow Green
Colour of flower violet White

24. 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.

25. Two copies of the same allele, such as two
dominant alleles.
One of each type of allele, one dominant and one
recessive.

27. 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.

28. 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.

29. 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.

31. A new form of plant resulting from cross or breeding
of different varieties of a plant is know as a hybrid
Characteristics that appear unchanged
generation after generation.

32. A condition in which the 2 members of an
allelic pair are similar. E.g. TT, tt.
A condition in which the 2 members of an
allelic pair are dissimilar. E.g. Tt.
Organisms produced as a result of sexual
reproduction

36. • A breeding experiment dealing with a
angle character is called a monohybrid
cross.
•Mendel first selected ‘Pure line’
plants(i.e. the plants that produced similar
traits generation after generation).

41. 

46.  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.

47. Allele or genes remain together and
segregate at the time of gamete formation.
This means that the alleles do not mix in
the hybrids.
This law is also known as law of purity of
gametes.

48. 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.

49. How do these traits get expressed?

50. 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
.

52.  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.

55. 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 .

57.  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”

59. FEATURES CHEMICAL EVOLUTION ORGANIC EVOLUTION
DEFINITION
It is the formation of the
complex organic compounds
from simple compound or
element.
It is formation of complex
form of life from simple
form of life.
TIME
OCCURRENCE
It occurred at the time of origin
of life
It is still occurring
REVERSIBILIT
Y
Irreversible reversible
SPEED OF
EVOLUTION
It is fast process It is slow process
INDEX WAS
A.I. Oparin Charles Robert Darwin

62. ACQUIRED TRAITS INHERITED TRAITS
These are the traits which are
developed in an individual due
to special conditions.
These are traits which are
passed from generation to
generation.
They cannot be transferred to
the progeny
They get transferred to be the
progeny.
They cannot direct evolution
e.g.. Low weight of starving
beetles.
They are helpful in evolution.
E.g.. Color of eyes and hair

63. To learn more about the acquired and inherited traits there are some
theories:
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??

64. Carolus Linnaeus – said that no species is new
i.e. each species originates from pre existing
species.

65. Theory of acquired and inherited
explained in his book namely philosophie
zoologique.
This theory states that use and disuse of an
organ leads to change in the organ. Which
is inherited by the offspring.
The favorable variations which remain for
longer period of time results in evolution
of new species.

67.  As We Know That Variation Arises During Sexual Reproduction
And It Is The Result Of Error And DNA Copying Now Take A Look
Some Consequences Of This Tendency.
 An Illustration - Consider The Following Example.
A Group Of Twelve Red Beetles Living In Bushes With Green
Leaves.
 Beetles In The Population Can Generate Variations Because These
Are Reproducing Sexually.
 Crow Can Eat The Beetles. The More Beetles The Crow Eat, The
Fewer Beetles Are Left For Reproduction

68. 1st situation 2nd situation 3rd situation
A green color variation
rises during reproduction
A blue color variation arises
during reproduction
Condition 1:
Appearance of plant disease in
the bushes.
One beetle
This blue beetle can pass the
blue color to its progeny
Amount of plant (leaf) material
for the beetles decreases
This green beetle can pass
the green color to its
progeny
Crow can see blue as well
red beetles on the green
leaves of bushes so can eat
them
Beetles are poorly nourished.
Observation 1
Observation- More
population compared to red
beetles.
conclusion
Beetles which survived are
mostly blue. This is by
chance.
Condition 2:
Appearance of plant disease in
the bushes.
Now consider the following situation:

69. 1st situation 2nd situation 3rd situation
Variation have survival
advantage
Rare variation came as a
common characteristics in
the population
Observation: population of
beetles grows slowly and
blue beetles are more in
number.
Conclusion: variation do not
have survival advantage.
Amount of plant( leaf) material
for the beetles increases.
Beetles are properly nourished.
In other words, frequency
of certain gene traits (genes
control the traits) changed
over generations. This is the
idea of evolution
Frequency of certain traits /
genes can be changed by
accidents in small
Observations 2:
Size of the saturated
increases to normal.
Now consider the following situation:

70.  Inheritance of the characters according
to darwin.
Charles Darwin set out on a voyage
when he was 22 years old.
He travelled by HMS beagle ship.
He visited many islands of south Africa,
Australia and Galapagos islands.
Name of his book is origin of species.
The theory presented by him is Called
THEORY OF NATURAL SELECTION OR
DARWINISM

71. FACTS CONSEQUENCES
I. Enormous rate of reproduction among
animals.
II. Constant number of animals of a
species.
Struggle for existence
I. Struggle for existence
II. Heritable variations
Survival of the fittest or natural selection
I. Struggle for existence
II. Continues environment changes
Continuous natural selection leading to
evolution of new species

72. 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
varies a dutch botanist.
According to him heritable variations arise when there is a change in
genes of the germplasm (protoplasm of germ cell).
 He called it mutation.

73.  J.B.S. Haldane, 1929, British scientist.
That life must have arisen on the
primitive earth from a collection of
chemicals.
 Atoms combined into inorganic
molecules, inorganic molecules into
simple organic compounds, simple
organic compounds into complex
organic compound, that were
necessary for life.

79. • A group of living organisms consisting of similar individuals
capable of exchanging genes or interbreeding.
• The origin of new species from the existing one due to
reproductive isolation of a part of its population is called
speciation.
•Some factor involves in the development of new species.

80. A species is a sexually
interbreeding group of
individuals separated
from other species by the
absence of genetic
exchange.
Cannot breed, different songs, different behavio

81.  Gene pool – Sum of all the
genes of all the members of a
species.
Speciation occurs when the
gene pool of a population is
somehow 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.

82.  Gene flow :–
It means the exchange of genetic material by interbreeding between
populations of the same species or between individuals within a
population. It increases the variation in the genetic composition of a
population

83.  Gene drift :– It is random change in the frequency of all alleles in
a population over successive generation due to errors in the gametes.
The process is rapid in smaller population.
Genetic drift can lead to accumulation of changes in the generations.

84.  NATURAL SELECTION: According to Darwin variations existed
between the individuals of a population and some natural phenomena
eliminated those individuals which were less adapted.
The surviving population would pass the hereditary advantageous
features to their offsprings.
With time this process would give rise to organisms different from the
original population and new species are formed.

86. ISOLATION:
When a population of a species splits into two, it cannot
reproduce with each other and forms a new species.
Example:
• When a population of beetles feed on bushes on a mountain range,
some may start feeding on nearby bushes finding entry into a new
subpopulation.
•They reproduce with them so genes enter in a new population.
Ultimately the two groups will be incapable of reproducing with each
other and a new species will be formed.

88. Artificial selection:
New species have been created by domesticated animal husbandry
(hybridisation).

89.  Classification:
Classification is the system of arrangement
in certain groups of subgroups on the basis
of hierarchies of certain characteristics
 The characteristics are the details of appearance
from structure, function and behavior phylogenetic
taxonomy is branch of classification on the basis of
evolutionary relationship on the basis of common
ancestry.

90. Cell is the basic structural and functional unit of life
Prokaryotic cell Eukaryotic cell
Unicellular Multicellular
Heterotrophs
Autotrophs
Skeletal inside the body Skeleton outside the body
Presence of nucleus
Complexity of organism
Mode of nutrition
Location and nature of skeleton

91. Studies on similarities in structure of different organisms suggests
that present from have evolved through a process of slow and
gradual change called evolution.

92. 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.
Forelimbs in vertebrates
SEAL BIRD BAT HORSE MAN
APPEARANCE Flippers Wings Patagia Elongated Thumb
Opposability
FUNTION Swimming Flying Support
Flying
Funning Grasping

94. Analogous organs:
• Those organs which have different origin and structural plan but
appear similar and perform similar functions are called analogous
organs.
•E.g. : Wing of an insect and a bird, hand of man & trunk of
element.

95. Vestigial organs:
• Those organs which no longer have function are called vestigial
organs.
•E.g. : vermiform appendix, ear muscles, third eyelid in man are
reduced and function less.

97. Evidences from palentology:
 Fossils: Fossils are the petrified remains and for impressions of
the hard parts of the extinct organism preserved in the
sedimentary rock or other media.
Paleontology – Study of fossils is known as paleontology.

98.  Let us start 100 million years ago. Some invertebrates on the
sea-bed 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 are buried in mud ,too. This mud is also compressed
in to rock, above the rock containing the earlier invertebrate
fossils.

99.  Again millions of years later, the
bodies of horse-like creatures dying in
the area are fossilised In rocks above
these earlier rocks.
Much later, by erosion or water
flow wears away some of the rock
and exposes the horse-like fossils. As
we dig deeper, we will find older and
older fossils.

100. Determination of the age of fossil:
• There are 3 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.
1. Using radioactive elements:
The age of a fossil is determined with the help of certain
radioactive element such as uranium present in the rock.
3. Carbon dating:
Carbon dioxide of air contains a small proportion of radioactive
carbon(C14).

102.  Evolutionary changes are fundamental characteristics of living
organisms .
It means that the similar looking structures may have different
ancestral designs.

103.  Eye- Eyes of insects, octopus and vertebrates have similar looks
but different structure and must have separate evolutionary origin
or different ancestral designs. Rudimentary eye can be useful to
some extent.
This can be explained by example of eye.

104.  The function of feathers was insulation cold weather later
feathers might have proved to be useful for the purpose of light.
Feathers:-

105.  Humans have developed different types of vegetables from the
wild cabbage by artificial selection.
Cabbage:-
Vegetable
evolved
Edible part
Cabbage Selection of fleshy terminal buds and short distance between
the leaves.
Brussels sprouts Selection for fleshy lateral.
Kohlrabi Selection for fleshy stem.
Kale Selection for large sized leaves so it is a leafy vegetables.
Broccoli Selection for leafy sized and arrested flower developments.
Cauliflower Selection for fleshy sterile flower.

109.  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 equated with progress because
of following reasons.

110. 1. In evolution older species are no eliminated during
formation of new species and most of older and simple
species still survive.
E.g. 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.

113.  Evolutionary history of man has been guilt from
the palaeontology (fossil studies) and molecular
biology( especially DNA changes).
For example:
It is not true that human beings have evolved
from chimpanzees.
Rathe 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.