Class X - Biology

2.  Genetics - Branch of biology which deals heredity and variation.
 Heredity – transfer of trait / character from one generation to
another generation.
for ex. Free and attached lobed, height body colour etc.
 Traits – inherited features/characters .
 Variation – difference among the individual of a species.
 If one bacterium divide forms two afterward four bacteria ,there
would be very minor differences between them. This differences
are due to small inaccuracies in DNA copying ,resulted to
Variation.
for ex. Real brothers and sisters does not have similar character (
except identical twins)
 Do all these variation in a species have equal chance of surviving
in the environment ? - Obliviously not. It depends upon the
nature of variation and selection of variants ( organism in which
variation occurred ) by environmental factors.
 Father of Genetics – Gregor Johann Mendel
(1822-1884)

3.  Cause of Variation –
i. Sexual reproduction
cause the greater
diversity and variation.
This is due to
crossing over takes place
during the meiosis cell
division at the time of
gamete formation .
ii. Mutation – change in
the structure or number
of chromosome .
iii. Genetic drift- change
in frequency of genes
without adaptation . Etc.

4. Mendel’s contribution in the field of
Genetics
 Gregor Johann Mendel was educated
in Monastery and working as Priest.
 He started the experiment on
Garden pea ( Pisum sativum) about
7 years i.e. 1856-1863 and proposed
the Law of inheritance by using the
knowledge of mathematics &
statistics.
 But he work remain unnoticed up to
1900 ,which was rediscovered by –
Hugo de Vries, Carl Correns, Eric von
Tschermak and called Mendel as a
“Father of Genetics “


5. Why the Mendel used Garden pea plant for his
experiment
1. Garden pea plant is bisexual (having male and female part )
2. Self pollination takes place but it is easy for cross-pollination.
3. Short life span
4. 7 pair of contrasting characters are available ( 14 different
varieties of G. pea)
For ex.
Character Dominant Recessive
i. Height Tall Dwarf
ii. Flower colour Violet white
iii. Flower position Axial Terminal
iv. Pod colour Green yellow
v. Pod shape Full constricted
vi. Seed colour Yellow green
vii. Seed shape Round wrinkled.

6. Terminology of Genetics
1. Factor – this term used by Mendel for the heredity unit, which further
replaced by term genes
2. Gene- It is the unit of heredity & have the information to express the
character.
3. Alleles- are the two forms of a single genes, which require to form a
single character.
4. Dominance – the character which expressed in F1 generation.
5. Recessive – the character which remain hidden in F1 generation.
6. Monohybrid cross- Study of inheritance of one contrasting
(opposite) character are called as monohybrid cross.
Monohybrid cross ratio – Phenotypic Ratio - 3 : 1
Genotypic Ratio - 1 : 2 : 1
7. Dihybrid Cross – Study of inheritance of two contrasting characters
are called as Dihybrid cross.
Dihybrid cross ratio – Phenotypic Ratio - 9 : 3 : 3 : 1
(Genotypic Ratio - 1 : 2 : 1 : 1: 4 : 2 : 1:2:2)
8. Phenotype – The external appearance of an individual
9. Genotype - Genetic make up of an individual

7. Rules for the inheritance of traits- Mendel’s Contribution /
Mendel’s Law of inheritance
 Monohybrid Cross - Study of inheritance of one contrasting
(opposite) character are called as monohybrid cross.
For ex. Cross between Tall pea plant with Dwarf pea plant.
Parents TT X tt
Gametes – G1 T t
F 1 Genn Tt Hybrid
Gametes – G2 T t
F 2 Genn
T t
T TT -
(Pure tall)
Tt -
(Hybrid tall)
t Tt -
(Hybrid
tall)
tt
(pure
dwarf)
Monohybrid cross ratio – Phenotypic 3 : 1 & Genotypic 1 : 2

9.  Dihybrid Cross - Study of inheritance of
two contrasting (opposite) character
simultaneously, are called as Dihybrid cross.
For ex. Cross between Round shape& yellow pea seed
plant with wrinkled & green pea seed plant.
Parents RRYY X rryy
Gametes – G1 RY ry
F 1 Genn RrYy Hybrid (Round, Yellow)
Gametes – G2 RY Ry rY ry
F 2 Genn

10. RY Ry rY ry
RY RRYY RRyY RrYY RrYy
Ry RRYy RRyy RrYy Rryy
rY RrYY RrYy rrYY rrYy
ry RrYy Rryy rrYy rryy
F 2 Generation
Dihybrid cross ratio - Phenotypic 9 : 3 : 3: 1
(Genotypic Ratio - 1 : 2 : 1 : 1: 4 : 2 : 1: 2:2 )

11. Mendel’s Law –
1. Law of Dominance – In F1 hybrid ,dominance alleles are
expressed and recessive alleles remain hidden.
For ex. Tt in which T is dominant and t remain hidden
(recessive).
2. Law of Segregation – At the time of gamete formation two
alleles segregate from each other without affecting the
other alleles.
For ex. T t hybrid - forms two types of gametes i.e. T & t
without affecting one another.
3. Law of Independent assortment – In dihybrid individual
two pair of alleles remain together, and segregate (
separate out ) from each other without affecting the other
alleles i.e. independent inheritance of traits (characters )
takes place.
For ex. Tall / short trait and Round /wrinkled trait
independently inherit.

12.  How do the Traits expressed ? Or
How does the mechanism of
heredity work ?
 Cell contains nucleus , which
contains thread like bodies called as
chromosomes . The chromosome
contains the DNA (Deoxyribose
nucleic acid ).
DNA have the genes ,which
provides the information for the
formation of Proteins.
 Cell Nucleus
Chromosomes DNA
Genes Proteins .

13.  How do proteins control the characteristics like
height in plant ?
 Genes present on DNA have the information to form
proteins.
To trigger the plant height, hormones are required .
To form these growth hormone ,there are requirement
of enzymes.
Enzymes are nothing but the protein & its formation
controlled by genes.
If the genes work efficiently , considerable amount of
proteins (enzyme ) forms which result to form lot of
hormones .It trigger the height and plant become tall.
Thus the genes control the characters ( traits) of
individual.

14.  Interpretation of Mendelian experiment to
explain the role of both the parents
During sexual reproduction each parent forms
germ cell (gamete) which have only one gene set i.e.
haploid.
After the fertilisation again two sets of alleles( one
from male and another from female parents) restore
the normal chromosome number as well as allelic
pair. In this way stability of the DNA of species takes
place.

15.  Sex determination –
The process of determining the sex of new born
individual before the birth is called as sex
determination.
 Different strategies for sex determination-
1.Role of environmental factors – like temperature
For ex.
(a) In Turtle (Chrysema picta ) – incubation at
High temperature forms female progeny.
(b) In Lizard ( Agama agama ) - incubation at
High temperature forms male progeny.

16.  2. Change of Sex by individual –
In snail , individual can change the sex .
It means sex is not genetically determined.
 3. Sex determination in human being –
In human being sex is largely determined genetically. It
means parents decide the sex of new born baby.
Human has two types of chromosomes – i .
Autosomes ii. Sex chromosomes.
i. Autosomes – these chromosomes controlled the body
characters.
ii. Sex chromosome – these chromosome determine the
sex. For ex. perfect pair of XX in Female and
mismatched pair of XY chromosome in Male in which
Y chromosome is short one .
 There are about 23 pairs of chromosome present in
human. Out of which 22 pairs are Autosomes and 1 pair
is sex chromosome ( XX / XY)

17. 
 female male
X X Y
50 % Female 50 % male
XY
XX
XX XY

18.  It means sex of new
born individual is
determined by father
and not by mother.

19.  Evolution –
 The process of forming today's
complex life from pre-existing
simple life by gradual changes
called as Evolution.
 This type of evolution in living
organism known as Organic
evolution.
This unfolding of organism or
gradual changes in pre-existing
organism took place through
variation during sexual
reproduction and error in DNA
copying.

20.  3 situations for Variation in population
 Two types of beetles – Red & Green lives in bushes of
green leaves.
 See the Figure 9.7 (page no.147 of T.B.)
1.There are more red beetles in the beginning & a few
green beetle. After the several generation –
 The no. of green beetles increased and red
beetles decreased because crow eaten most of the red
beetle which were easily visualise while green beetle
match with green background of leaves. This type of
selection is the selection of individual by Natural
selection.

21. 2. In second situation there are two types of beetles –
Red and blue.
 Both types of beetles can visualise by crow & can
eat any type of beetle . But at this point elephant
comes and stamp the bushes where most of the
beetles lives. It result to kill the most of beetles.
 By chance a few blue beetles survived & their
population increased.
 This type of selection of individual is due to -
Genetic drift. In which accidental survival benefits
of one colour beetle took place . It means diversity
without adaptation takes place

22.  3. In third situation- bushes start
suffering from plant diseases,
resulted to reduce the plant leaf
material .
It result to poorly nourishment
of beetle and decrease the average
weight .
After a few years plant disease
eliminated and again the weight of
beetle increases.
It means change in non-
reproductive cell cannot inherit to
next generation.

23.  Theories of Evolution –
Two main theories
 1. Theory of Inheritance of
Acquired characters Or
Lamarckism .
 2.Theory of Natural
selection or Darwinism .

24.  1. Theory of Inheritance of Acquired
characters Or Lamarckism
 Lamarck, Jean-Baptiste proposed the
theory of inheritance of acquired
characters. According to him useful
organs leads to acquire and inherit it to
next generation while disuse leads to
disappear of character.
 For ex. Extension of Giraf’s neck.
 But , this theory disapproved by Auguste
Weismann. He cuts the tail of rats for
about 21st generation even though he
found the tail in 22nd generation.

25.  2.Theory of Natural selection or
Darwinism –
Charles Robert Darwin (1809-1882) observed
the nature during his 5 years voyage to South
America and Galapagos islands by H.M.S.Beagle
ship. After his voyage he formulated the theory
of Natural selection.
Main points of Theory of Natural Selection –
a) High rate of reproduction
b) Struggle for existence
c) Variation
d) Survival of fittest
e) Selection by Nature.
 But Darwin could not explain the reasons of
Variation.
 The two gentleman – Mendel and Darwin did not
know each other.
 Darwin was conducted the study and explain the
role of Earthworms in soil fertility.
 Darwinism replaced by New-Darwinism
theory in which reasons of variation
included.

26.  Origin of life on Earth –
J.B.S.Haldane suggested
that the life is originated on
earth from inorganic
molecules in 1929 .
He explained that the
condition of earth (before 3
billion year ago) at the time of
origin of life was not like
today.
That time there was high
temperature, reducing
atmosphere with more amount
of N2 , CH 4,NH3,,H2O
vapours,CO2 etc.
Massive thunderstorm &
lightning might have formed
complex organic molecules
which required to form the
life. In this way primitive life
form .In this way there might
have been abiogenesis took
place.

27.  In 1953,Stanley L. Miller and
Harold C. Urey experimentally
proved the Haldane hypothesis.
They created similar condition
of primitive atmosphere in a
laboratory by using closed
flasks.
 They had taken the gases like N2
, CH4,NH3,H2S in one closed
flask with electric discharge to
maintain the
temperature just below 100 0C
and water vapour in other flask.
 They kept these assembly for a
week and at the end they
observed that 15 % of carbon
from methane converted to
simple compounds and formed
amino acids.
 From these experiment ,it was
concluded that the life
originated about 3 billions years
ago

28.  Micro-evolution- The processes which makes small
changes in the characteristics of a particular
species, though it is small but are significant.
 The micro-evolution does not forms the new
species.

29.  Speciation- The process of formation of new species
called as speciation.
 Factors causing speciation –
1. Gene flow – The migration of organisms from one
area to other result to migrate the genes .This
population reproduce with local population & create
a new species.
This kind of flow of genes to create new
species known as Gene flow.
If river or ocean or mountain range or any obstacle
present between two sub population the gene flow
decreases .
For ex. Beetles feed on small bushes do not travel far &
reproduce with neighborhood populations only . But
their migration with one or more reasons like picking
by crow result to flow the gene.
2.Genetic drift – The change in frequency without any
adaptation called as genetic drift.
For ex. Elephant stamped increase the no. of blue
beetle by chance but at other places no. of blue
beetles may be high.
3. Natural selection- situation 1
(The no. of green beetles increased and red beetles
decreased because crow eaten most of the red beetle
which were easily visualise while green beetle match
with green background of leaves. This type of
selection is the selection of individual by Natural
selection.)
4.Mutation-Abrupt change in the structure or number of
chromosome leads to cause the change which are
inherited & forms the new species.

30.  Evolution and Classification-
To study the evolution, we have
study the characters which are more
closely related to common ancestor.
For ex.-
i. Brothers and sisters are closely related to
parents.
ii. Cousin & a girl also related because they
related to grand parent but less than
brother and sister.
 Evolution - The process of forming
today's complex life from pre-existing
simple life by gradual changes called
as Evolution.
 First life originated from non-living matter
( Abiogenesis) in water & afterward
organic evolution takes place.

31.  Evidences of evolution –
 A. Morphological evidence
 B. Palentological evidences
 C. Genetic evidences or molecular phylogeny.
 D. Embryological evidences.
 A. Morphological evidence - Common features
of different organism provides evidences for
evolution.
For ex.
1. Homologous organs
2. Analogous organs
3. Vestigial organs

32. 1. Homologous organs- The
organs which have similar
basic structure & common
origin but the functions are
different.
For ex.
a) Fore limb of frog (hopping),
lizard (climbing),
bird (flying)
human (performing work)
b) Thorn of bougainvillea
,tendril of cucurbita.etc.

33. 2.Analogous organs- The organs
which have different basic
structure & origin but the
functions are similar.
For ex.
a) Bats wings ,birds wings
- bats wings are the skin fold
which stretched between
elongated fingers ,while birds
wings are feathery covering
but both have same function.
b) Eyes of octopus & mammals
c) Sweet potato and Potato etc.

34. 3.Vestigial organs- the
functionless organs
of body.
For ex. Vermiform
appendix, nictating
membrane, ear
pinna muscles etc.

35.  B. Palentological
evidences –
Paleontology- Study of
fossils known as
Paleontology.
Fossils – The dead remains
of organism which were
present earlier or
preserved the traces of
living organisms.
The study of fossils
provides the evidence of
evolution.
For ex. Archaeopteryx –
have the characteristics of
birds and reptiles.
Dinosaur Skulls
Archaeopteryx
Fossilized Trilobite

36.  How do fossils age can
estimate ?
 Fossils found closer to
upper surface are more
recent than the fossil found
deeper layer
Detection of radioactive
isotopes.

37.  C . Genetic evidences or
molecular phylogeny –
 Study of change in the DNA
during the reproduction can
be estimated by knowing the
amount of DNA changed
during the formation of next
generation.

38.  Evolution by stages-
How the complicated organs generated by a
single DNA change ?
 Complex organs created bit by bit over the
generations to give the fitness advantage.
 For ex. Eyes in insects ,Octopus, Vertebrates
.
-Eyes of invertebrates like flatworm
(Planaria) are simple & just eye spot to
detect the light.
 Feathers- provides insulation in cold
weather .
for ex. some dinosaurs had feather but
it could not used for flying.
while, in birds feathers adapted for
flying. It means birds are closely related to
reptiles.
The analysis of organs in fossils provides
guesses about what happened in history.

39.  Artificial selection of wild cabbage –
Current example of generation of new
variety by human is the artificial
selection of wild cabbage.
 Human cultivated wild cabbage for
about more than two thousand years for
food.
 Some farmers want it two have very short
distance between leaves – hence they
selected Cabbage.
 Some farmer wanted arrested flower
development have bred –Broccoli.
 Some required sterile flower & have
made – Cauliflower .
 Some required swollen parts – Kohlrabi.
 Some required larger leaves with leafy
vegetable – Kale.
In this human selected the wild
cabbage artificially i.e. Artificial
selection & rather than natural selection.
Cauliflower
Broccoli.
Cabbage
Kale.
Wild
cabbage
Kohlrabi.

40.  Evolution should not be
equated with “Progress” –
 If one species eliminated
and new species emerged
(originated), it does not
mean old species
disappear . But ,it depends
on environment.
 The formation of
population ( new species)
is due to natural selection
,genetic drift etc.

41. Wrong concept of evolution – It is not true that
human evolved from Chimpanzees – but both
have common ancestor and have their separate
way of evolution
 Evolution mean not the real progress but it is
simply the generation of diversity and shaping
the diversity by environmental selection.
 Human being are not at the Pinnacle of evolution
but they are simply one species.
 Older species does not mean inefficient species.

42.  Human Evolution –
Tools for tracing
evolution –
1.Excavation – digging to
take out the fossils
2.Time-dating -Detection
of radioactive isotopes.
3.Study of fossils
4.Determining the
sequence of DNA.

43.  Human races-
People talk about the human races like skin colours
i.e. white,black,brown,yellow etc.
The study of evolution of human being indicates
that all of us belong to a single species that
evolved in Africa and migrants slowly to West
Asia ,then to Central Asia Eurasia, South Asia
,East Asia .
Then travelled down the islands of Indonesia
,Phillipines, Australia & then to America .
PRESENTATION PREPARED BY-
SH. R.S.CHANDANSHIV,
PRINCIPAL ,
JNV,WASHIM
Contact - ravi_chandanshiv@yahoo.com
08600516929