Download - Heridity and evolution
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HERIDITY
EVOLUTIONAND
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ACCUMULATION OF VARIATION
DURING REPRODUCTION
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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.
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HEREDITY
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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.
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GREGOR JOHANN MENDEL
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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.
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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.
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MENDEL’S EXPERIMENTS
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Mendel used a number of contrasting visible characters of garden peas – round/wrinkled
seeds, tall/short plants, white/violet flowers and so on.
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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.
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MENDEL’S FIRST EXPERIMENT
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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.
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AT FIRST MENDEL CROSS-POLLINATED TALL AND SHORT PEA PLANTS OF PURE BREED.
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(TT)
(tt)
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IN RESULT, ALL THE OFFSPRING WERE TALL. HE NAMED THEM F1
GENERATION.
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WHEN THE PLANTS OF F1 GENERATION WERE FULLY
GROWN HE ALLOWED THEM TO SELF-POLLINATE.
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RESULT :- THE PLANTS IN THE F2 GENERATION WERE A MIX OF TALL AND
SHORT PLANTS.
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CROSS POLLINATION
SELF POLLINATION
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The result of monohybrid cross enabled Mendel to formulate
the first law of inheritance which is called the law of
segregation.
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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.
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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
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MENDEL’S SECOND EXPERIMENT
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For dihybrid inheritance Mendel chose two pairs of contrasting characteristics
which were shape and colour of seeds.
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WRINKLED – GREEN SEEDS
The two types of seeds were:-
ROUND – YELLOW SEEDS
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At first Mendel crossed pure breed pea plants having round-yellow seeds with pure breed
pea plant having wrinkled-green seeds.
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ROUND – YELLOW
PEA
WRINKLED – GREEN PEA
RR yyrrYY
RRYY rryy
ROUND YELLOW WRINKLED GREEN
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IN RESULT, ALL THE OFFSPRING WERE ROUND – YELLOW. HE
NAMED THEM F1 GENERATION.
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THEN HE ALLOWED THE PLANTS OF F1 GENERATION TO CROSS BREED BY SELF
POLLINATION.
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RESULT :- The offspring's in the f2 generation were having different
combinations of shape and colour.
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CROSS POLLINATION
SELF POLLINATION
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The result of dihybrid cross enabled Mendel to formulate the second law of inheritance
which is called the law of independent assortment.
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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.
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Round-Yellow
RYRY ryry
RrYy RrYy RrYy RrYy
Round-Yellow
Round-Yellow Round-Yellow Round-Yellow
Wrinkled-Green
rY ryRyRY rY ryRyRY
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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
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Ratio:- 9 : 3 : 3 : 1RoundYellow
RoundGreen
WrinkledYellow
WrinkledGreen
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TRANSMISSION OF CHARACTERSTICS (OR TRAITS) TO
PROGONY
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GENES ARE RESPONSIBLE FOR THE CHARACTERSTIC FEATURES
(OR TRAITS) OF AN ORGANISM:- PLANTS OR
ANIMALS
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The characteristics or traits of parents are transmitted to
their progeny through genes present on their chromosomes
during the process of sexual reproduction.
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INHERITANCE OF BLOOD GROUPS
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A PERSON HAS ONE OF THE FOUR BLOOD GROUPS :
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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.
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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.
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GENOTYPE BLOOD GROUP
IA IA
IA IOOR AIB IB
IB IOOR B
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GENOTYPE BLOOD GROUP
IA IB AB
IO IO O
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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.
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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.
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x xx y
Mother
Father
XX XY
Girl Boy
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Acquired traits
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A trait (or characteristic) of an organism which is ‘not inherited’ but develops in
response to the environment is called an
acquired trait.
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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.
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Rats with full tails
The tails of mice are cut off
Rats with full tails in second
generation
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INHERITED TRAITS
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A TRAIT OF AN ORGANISM WHICH IS
CAUSED BY A CHANGE IN ITS GENES IS CALLED AN
INHERITED TRAIT.
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EVOLUTION IS THE SEQUENCE OF GRADUAL CHANGES THAT TAKE PLACE IN THE PRIMITIVE ORGANISMS OVER MILLIONS
OF YEARS IN WHICH NEW SPECIES ARE PRODUCED.
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MILLIONS OF YEAR
BIG LIZARD
FOLDS OF AKIN DEVELOPED BETWEEN FEET
DEVELOPES INTO PTEROSAUR (a ancient flying reptile)
MILLIONS OF YEAR
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Evidences of evolution
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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
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HOMOLOGOUS ORGANS
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Those organs which have the same basic structure
(or same basic design) but different functions are called homologous
organs.
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HUMANLIZARD
FROG
BAT BIRD
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ANALOGOUS ORGANS
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The organs which have different basic structure
but have similar appearance and perform
similar functions are analogous organs.
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WING OF BIRDWING OF INSECT
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FOSSILS
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THE REMAINS (OR IMPRESSIONS) OF DEAD
ANIMALS OR PLANTS THAT LIVED IN THE REMOTE PAST
ARE KNOWN AS FOSSILS.
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AMMONITE TRILOBITE
DINOSAUR SKULL
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FORMATION OF FOSSILS
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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.
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DRAWIN’S THEORY OF EVOLUTION
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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’.
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Darwin's theory of evolution can be
described as follows :-
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Within any population, there is natural variation. Some individuals have more variations than others.
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Even though all species produce a large number of
offsprings, populations remain fairly constant naturally.
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This is due to the struggle between members of the same
species and different species for food, space and mate.
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The struggle for survival with in populations eliminates the unfit
individuals. The fit individuals survive and reproduce.
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The individuals having favourable variations pass on
these variations to their progeny from generation to generation.
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These variations when accumulated over a long
period of time, lead to the origin of a new species.
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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.
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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.
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The process by which new species develop from
existing species is known as speciation.
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IMPORTANT FACTORS WHICH COULD LEAD TO
THE RISE OF A NEW SPECIES
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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.
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Genetic drift caused by drastic changes in the
frequencies of particular genes by chance alone.
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Variations caused in individuals due to natural selection.
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EVOLUTION OF STAGES
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The complex body organs of animals such as eyes
have been created in ‘stages’ over many
generations.
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Evolution of eyes
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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.
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EVOLUTION OF FEATHERS
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Sometimes an evolutionary change produced in an
organism for one purpose later on becomes more useful for an
entirely different function.
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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.
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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.
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Modification of a species by human intervention so that certain desirable traits are represented in successive
generations.
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Some farmers wanted to have very short distances between the leaves of wild cabbage and produced the
common variety of ‘cabbage’.
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When farmers opted for the arrested flower development of wild cabbage, it led to the
production of ‘Broccoli’.
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Some farmers went in for sterile flowers of wild cabbage and developed another variety of cabbage called ‘cauliflower’.
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When farmers opted for the swollen parts of wild cabbage, it led to evolution of a yet another
variety of cabbage called ‘kohlrabi’.
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And when farmers wanted to grow leaves of wild cabbage, they ended
up producing a leafy vegetable called ‘kale’.
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EVOLUTION SHOULD NOT BE EQUATED WITH
PROGRESS.
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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.
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HUMAN EVOLUTION
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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.
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ANKURX-C23
AMBA