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CHAPTER – 9

Heredity and Evolution
Genetics : Branch of science that deals with Heredity and variation
...

Variation : The differences among the individuals of a species/ population are
called variations
...
Mendel used a number
of contrasting characters for garden pea
...
(SEVEN PARTS)
CHARACTER
DOMINANT
RECESSIVE
TRAIT
TRAIT
Flower colour
Purple
White
Flower position
Axial
Terminal
Yellow
Green
Seed colour
Round
Wrinkled
Seed shape
Inflated
Constricted
Pod shape
Green
Yellow
Pod colour
Tall
Dwarf
Height of plant
Seven pairs of contrasting characters in Garden
Pea
Mendels Experiments : Mendel conducted a series of experiments in which he
crossed the pollinated plants to study one character (at a time)
Monohybrid Cross :
Cross between two pea plants with one pair (monohybrid cross) contrasting
characters
Example : Tall / Short Plants
...

[Hybrid]

Phenotypic ratio : 3:1
Genotypic ratio : 1:2:1
Phenotype fi
Physical appearance [Tall or Short]
Genotype fi up [TT, Tt or tt]
Genetic make
Observations :

1
...
F2 progeny ¼ were short
3
...
TT and Tt both are tall plants while tt is a short plant
...
A single copy of T is enough to make the plant tall, while
both copies have to be 't' for the plant to be short
...
Characters/Traits like 'T' are called dominant trait (because
it express itself) 't' are recessive trait (because it remains
supressed)

Dihybrid Cross : A cross macle between two plants having two pairs of
contrasting characters is called dihybrid cross
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When RRYY was crossed with rryy in F1 generation all
were Rr Yy round and yellow seeds
...
Self pollination of F1 plants gave parental phenotype + two
mixtures (recombinants) Round wrinkled, green yellow :
seeds plants appeared in the ratio of 9:3:3:1

Conclussions :

1
...
Occurence of new phenotypic combinations show that
genes for round and yellow seeds are inherited
independently of each other
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Genetic
In some animals like humans gender or
individual is determined by a pair of
chromosome called sex chromosome

eg
...
Out of
these 22 chromosomes pairs are called autosomes and the last pair of
chromosomes that help in deciding gender of that individual are called sex
chromosome
...
All children
will in herit an X chromosome from their mother regardless whether they are boys
or girls
...

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Evolution
SITUATION-I
Group of red beetles
Colour variation arises during reproduction
All beetles red except
one that is green

One beetle Green
Reproduction

Crows feed on red beetle

Progeny beetles green

No
...
This natural selection is exerted
by crows resulting in adaptations in the beetles to fit better in their environment

SITUATION-II
Group of red beetles
Reproduction
All beetles are red except one
that is blue
Reproduces

One blue beetle
Reproduces

Number of red beetle
increases

No
...


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Situation 2 : Blue beetles did not get survivals advantage
...

From this we can conclude that accidents can change the frequency of some genes
even if they do not get survival advantage: This is called genetic drift and it leads to
variation
...
It leads to diversity without any adaptation

SITUATION-III
Group of red beetles
Habitat of beetles (bushes)
Suffer from plant disease
Average weight of beetles
decreases due to poor nourishment
No of beetles kept on reducing
Later plant disease gets eliminated
Number and average weight of the beetles
increases again
Situation 3 : No genetic change has occured in the population of beetle
...
These are the traits which are
developed in an individual due
to special conditions

1
...


2
...
They get transferred to the
progeny
...
They cannot direct evolution

3
...


eg
...


eg
...
eg
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Speciation : it is the process of formation of new species
...

Geneflow : It is exchange of genetic material by interbreeding between
populations of same species or individuals
WAYS BY WHICH SPECIATION TAKES PLACE
Speciation takes place when variation is combined with geographical isolation
...

*Natural Selection : The process by which nature selects and consolidate those
organisms which are more suitably adapted and posesses favorable variations
POPULATION Z
Sub Population
Z1

GEOGRAPHICAL
BARRIER
ISOLATION
(River, Mountain)

Sub Population
Z2

Over many-many generations

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Results in Accumulation of different variations in
Sub population Z1 and Z2
Genetic drift
Natural selection
Sub population Z1 and Z2 incapable
of interbreeding
Reproductive
Barrier
Formation of
Formation of
new Species 1
new Species 2
Genetic drift takes place due to
a) Severe changes in the DNA
b) Change in number of chromosomes
Evolution and classification
Both evolution and classification
are interlinked
...
Classification of species is
reflection of their
evolutionary relationship
...
The more characteristic two
species have in common the
more closely they are
related
...
The more closely they are
related, the more recently
they have a common
ancestor
...
S i m i l a r i t i e s a m o n g
organisms allow us to group
them together and to study
their characteristic

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Tracing Evolutionary Relationships
(Evidences of Evolution)
I
...
These are
the organs that have same basic structural plan and origin but different
functions
...
Analogous Organs : These are the organs that have different origin and
structural plan but same function example :
Design different
Wings of bat fi
elongated fingers with skin folds
same function
ie
...
Fossils : (Palaeontological evidences)
The remains and relics of dead organisms of the past
...

FOSSILS ARE PRESERVED TRACES OF LIVING ORGANISMS
Eg
...


Deeper the fossil, older it is
...
Detecting the ratios of different of
the same element in the fossil
material ie Radio-carbon dating
...

2
...

4
...

6
...

I
...

enough to
Flat worm has rudimentary eyes give fitness
advantage
Insects have compound eyes
Humans have binocular eyes

II
...

Example :
Dinosaurs had feathers, but could not fly using feathers
...

Artificial Selection :
Humans have been a powerful agent in modifying wild species to suit their own
requirement through out ages by using artificial selection
...
(ii)
Wheat (many varieties obtained due to artificial selection)

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WILD
CABBAGE

KALE

CABBAGE
with larger
leaves
with short distance
between the leaves
BROCCOLI

KOHL RABI
CAULIFLOWER

Has sterile
flowers

Arrested flower
development

With Swollen
parts

Molecular Phylogeny :
?
It is based on the idea that changes in DNA during reproduction are the basic

events in evolution
?
Organisms which are more distantly related will accumulate greater

differences in their DNA

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Human Evolution
Tools to Study Human Evolutionary Relationship

Excavating

Time dating

Fossils

Determining
DNA
Sequences

Although there is great diversity of human forms all over the world get all humans
are a single species
GENETIC FOOTPRINTS OF HUMANS
Hundreds/thousand of years ago
Earliest members arose in Africa

East Asia
South Africa

Africa
Philippines

Island
of
Indonesia

West
Asia

Central
Asia

Australia
Eurasia

?
They did'nt go in a single line
?
They went forward and backward
? in and out of Africa
Moved
?
Sometimes came back to mix with each other
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Define variation

2
...


What is dominant trait
...


What are genes?

5
...


If an individual has XX chromosome [22+XX] will that individual be male
or female
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Which plant Mendel had choosen for his experiments
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How do Mendel's experiment show that traits may be dominant or recessive?

9
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Short Answers (2 Marks)
1
...


2
...


What is speciation? What factors lead to formation of a new species
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Explain the mechanism of sex determination in humans
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Differentiate between homologous and analogous organs
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6
...
What are the units of inheritance

7
...


Explain monohydrid cross by taking tall and dwarf plants
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Long Answer (5 Marks each)
1
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2
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