HERIDITY

EVOLUTIONAND

ACCUMULATION OF VARIATION

DURING REPRODUCTION

Inheritance from the previous generation provides both a common basic body

design, and subtle changes in it, for the next generation. The second generation

will have differences that they inherit from the first generation, as well as newly

created differences.

HEREDITY

Heredity is the passing of traits to offspring from its parents or

ancestor. This is the process by which an offspring cell or organism acquires or becomes predisposed to the characteristics of its parent

cell or organism.

GREGOR JOHANN MENDEL

Gregor Johann Mendel (July 20, 1822 – January 6, 1884) was a German-speaking Silesian

scientist and Augustinian friar who gained posthumous fame as the founder of the new science of

genetics.

Mendel worked out the main rules of inheritance. Many others had studied the

inheritance of trait earlier, but Mendel blended his knowledge of science and

mathematics and was the first one to keep count of individuals exhibiting a particular trait in each generation. This helped him

to arrive at the laws of inheritance.

MENDEL’S EXPERIMENTS

Mendel used a number of contrasting visible characters of garden peas – round/wrinkled

seeds, tall/short plants, white/violet flowers and so on.

Mendel used Pea plant for his experiment, which are usually self

pollinating even when they are alone. He selected pea plant so

that he could control and change their self-pollination to cross-pollination. He called them ‘P’

generation.

MENDEL’S FIRST EXPERIMENT

He started with pure breed plants for mono hybrid

inheritance. He saw that even generation after generation,

produced plants looked identical to the parent plant.

AT FIRST MENDEL CROSS-POLLINATED TALL AND SHORT PEA PLANTS OF PURE BREED.

(TT)

(tt)

IN RESULT, ALL THE OFFSPRING WERE TALL. HE NAMED THEM F1

GENERATION.

WHEN THE PLANTS OF F1 GENERATION WERE FULLY

GROWN HE ALLOWED THEM TO SELF-POLLINATE.

RESULT :- THE PLANTS IN THE F2 GENERATION WERE A MIX OF TALL AND

SHORT PLANTS.

CROSS POLLINATION

SELF POLLINATION

The result of monohybrid cross enabled Mendel to formulate

the first law of inheritance which is called the law of

segregation.

According to law of segregation : The

characteristics of an organism are determined by internal factors which occur in pairs.

Only one of a pair of such factors can be present in a

single gamete.

TALL PLANT

TT tt

Tt Tt Tt Tt

tT tT

TT Tt Tt tt

TALL PLANT

TALL PLANT TALL PLANT TALL PLANT

SMALL PLANT

TALL PLANT TALL PLANT TALL PLANT SMALL PLANT

MENDEL’S SECOND EXPERIMENT

For dihybrid inheritance Mendel chose two pairs of contrasting characteristics

which were shape and colour of seeds.

WRINKLED – GREEN SEEDS

The two types of seeds were:-

ROUND – YELLOW SEEDS

At first Mendel crossed pure breed pea plants having round-yellow seeds with pure breed

pea plant having wrinkled-green seeds.

ROUND – YELLOW

PEA

WRINKLED – GREEN PEA

RR yyrrYY

RRYY rryy

ROUND YELLOW WRINKLED GREEN

IN RESULT, ALL THE OFFSPRING WERE ROUND – YELLOW. HE

NAMED THEM F1 GENERATION.

THEN HE ALLOWED THE PLANTS OF F1 GENERATION TO CROSS BREED BY SELF

POLLINATION.

RESULT :- The offspring's in the f2 generation were having different

combinations of shape and colour.

CROSS POLLINATION

SELF POLLINATION

The result of dihybrid cross enabled Mendel to formulate the second law of inheritance

which is called the law of independent assortment.

According to law of independent assortment : In the inheritance of more than

one pair of traits in across simultaneously, the factors responsible for each pair of

traits are distributed independently to the gametes.

Round-Yellow

RYRY ryry

RrYy RrYy RrYy RrYy

Round-Yellow

Round-Yellow Round-Yellow Round-Yellow

Wrinkled-Green

rY ryRyRY rY ryRyRY

Ry

rY

ry

RY

rY ryRyRY

RRYYRoundYellow

RRYyRoundYellow

RrYYRoundYellow

RrYyRoundYellow

RRYyRoundYellow

RRyyRoundGreen

RrYyRoundYellow

RryyRoundGreen

RrYYRoundYellow

RrYyRoundYellow

rrYYWrinkled

Yellow

rrYyWrinkled

Yellow

RrYyRoundYellow

RryyRoundGreen

rrYyWrinkled

Yellow

rryyWrinkled

Green

Ratio:- 9 : 3 : 3 : 1RoundYellow

RoundGreen

WrinkledYellow

WrinkledGreen

TRANSMISSION OF CHARACTERSTICS (OR TRAITS) TO

PROGONY

GENES ARE RESPONSIBLE FOR THE CHARACTERSTIC FEATURES

(OR TRAITS) OF AN ORGANISM:- PLANTS OR

ANIMALS

The characteristics or traits of parents are transmitted to

their progeny through genes present on their chromosomes

during the process of sexual reproduction.

INHERITANCE OF BLOOD GROUPS

A PERSON HAS ONE OF THE FOUR BLOOD GROUPS :

This blood group system is controlled by a gene which has three different forms denoted by the symbols IA,IB and IO. The

genes IA and IB show no dominance over each other. But they are dominant over

gene IO.

Although there are three gene forms for blood, but anyone person can have only two of

them. So, the blood group of a person depends on which two

forms of the genes he possesses.

GENOTYPE BLOOD GROUP

IA IA

IA IOOR AIB IB

IB IOOR B

GENOTYPE BLOOD GROUP

IA IB AB

IO IO O

A person can have a male sex or a female sex. The process by

which the sex of a person is determined is called sex

determination. Genetics is involved in the determination

of the sex of a person.

The chromosomes which determine the sex of a person are called sex chromosomes.

There are two types of sex chromosomes, one is called X chromosome and the other is

called Y chromosome.

x xx y

Mother

Father

XX XY

Girl Boy

Acquired traits

A trait (or characteristic) of an organism which is ‘not inherited’ but develops in

response to the environment is called an

acquired trait.

The acquired traits of organisms cannot be passed on to their future generations. Only those traits can

be transmitted to future generations in which changes have

occurred in the genes present in reproductive cells of parent

organism.

Rats with full tails

The tails of mice are cut off

Rats with full tails in second

generation

INHERITED TRAITS

A TRAIT OF AN ORGANISM WHICH IS

CAUSED BY A CHANGE IN ITS GENES IS CALLED AN

INHERITED TRAIT.

EVOLUTION IS THE SEQUENCE OF GRADUAL CHANGES THAT TAKE PLACE IN THE PRIMITIVE ORGANISMS OVER MILLIONS

OF YEARS IN WHICH NEW SPECIES ARE PRODUCED.

MILLIONS OF YEAR

BIG LIZARD

FOLDS OF AKIN DEVELOPED BETWEEN FEET

DEVELOPES INTO PTEROSAUR (a ancient flying reptile)

MILLIONS OF YEAR

Evidences of evolution

The more characteristics two species have in common, the more

closely they are related. Some important sources which provide

evidences for evolution are :-

1. HOMOLOGOUS ORGANS2. ANALOGOUS ORGANS3. FOSSILS

HOMOLOGOUS ORGANS

Those organs which have the same basic structure

(or same basic design) but different functions are called homologous

organs.

HUMANLIZARD

FROG

BAT BIRD

ANALOGOUS ORGANS

The organs which have different basic structure

but have similar appearance and perform

similar functions are analogous organs.

WING OF BIRDWING OF INSECT

FOSSILS

THE REMAINS (OR IMPRESSIONS) OF DEAD

ANIMALS OR PLANTS THAT LIVED IN THE REMOTE PAST

ARE KNOWN AS FOSSILS.

AMMONITE TRILOBITE

DINOSAUR SKULL

FORMATION OF FOSSILS

When organism die, their bodies get decomposed by the

action of micro-organism. Sometimes conditions of

environment do not let the body to decompose properly,

thus forming a fossil.

DRAWIN’S THEORY OF EVOLUTION

Charles Robert Darwin gave the theory of evolution in his famous book ‘the origin of species’. This

theory is known as ‘The theory of natural selection’.

Darwin's theory of evolution can be

described as follows :-

Within any population, there is natural variation. Some individuals have more 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 with in populations eliminates the unfit

individuals. The fit individuals survive and reproduce.

The individuals having favourable 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 a new species.

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 offspring, and those characteristics which do not help are not passed on.

A species is a population of organisms consisting of similar

individuals which can breed together and produce fertile offspring . Species can be of

plants or of animals.

The process by which new species develop from

existing species is known as speciation.

IMPORTANT FACTORS WHICH COULD LEAD TO

THE RISE OF A NEW SPECIES

Geographical isolation of a population caused by various types of barriers. The geographical isolation leads to reproductive isolation due to which there is no flow of genes between separated groups of population.

Genetic drift caused by drastic changes in the

frequencies of particular genes by chance alone.

Variations caused in individuals due to natural selection.

EVOLUTION OF STAGES

The complex body organs of animals such as eyes

have been created in ‘stages’ over many

generations.

Evolution of eyes

First of all the rudimentary eye like that of flatworm was

formed (they can only detect light). From this more and

more complex eyes were then evolved in in various

organisms.

EVOLUTION OF FEATHERS

Sometimes an evolutionary change produced in an

organism for one purpose later on becomes more useful for an

entirely different function.

For example, birds evolved feathers as a mean of providing insulation to

their bodies in cold weather but later on these feathers became useful for the purpose of flying.

Even dinosaurs had feathers though they could not fly by using

these feathers. The presence of feathers on birds tells us that the birds are very closely related to

dinosaurs i.e. reptiles.

Modification of a species by human intervention so that certain desirable traits are represented in successive

generations.

Some farmers wanted to have very short distances between the leaves of wild cabbage and produced the

common variety of ‘cabbage’.

When farmers opted for the arrested flower development of wild cabbage, it led to the

production of ‘Broccoli’.

Some farmers went in for sterile flowers of wild cabbage and developed another variety of cabbage called ‘cauliflower’.

When farmers opted for the swollen parts of wild cabbage, it led to evolution of a yet another

variety of cabbage called ‘kohlrabi’.

And when farmers wanted to grow leaves of wild cabbage, they ended

up producing a leafy vegetable called ‘kale’.

EVOLUTION SHOULD NOT BE EQUATED WITH

PROGRESS.

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 the environmental

selection. The only progress is more and more complex body design. No species is

eliminated. A new species is emerged.

HUMAN EVOLUTION

Where we have lived for the past few thousand years, we all come from Africa.

The earliest members of the human species, Homo sapiens, can be traced there. Our genetic footprints can be

traced back to our African roots. Some of our ancestors left Africa while others

stayed on.

ANKURX-C23

AMBA