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8. HEREDITY
(FROM PARENT TO PROGENY)
Heridity :- Lesson related 1, 2, 4 marks
Activities Question and
Transmission of characters from parent to offspring is called Heredity. videos Answers PDF
pl.scan QR
The characteristics of parents transmit from parents to progeny through ‘genes’ pl.scan QR
which are present on the chromosomes during the process of reproduction.
Variations :-
Differences in characters within very closely related groups of organisms are called varia-
tions.
Ex :- 1. Variations in cows are ...
White coloured - spotted - Brown - Black
Long horns - Short horns - horn less
Height - Dwarf - Medium height
Long tail - Short tail
more milk giving - less milk giving etc . . .
2. Variations in human beings ...
Curly hair - Soft hair
Black eyes - Blue eyes
Long - Short - Medium
Black colour - while colour etc . . .
Sexual reproduction and errors (mutations) in DNA copying leads to variations in off springs.
Variations are necessary for organic evolution.
Variations increase the chance of its survival in the changing environment.
Ex :- Variations in beetle population :-
Let us consider a group of red beetles lives in bushes on green leaves.
Crows identify and eat them easily due to red colour.
So, the population of red beetles is slowly reduced.
Green beetles are produced from red beetles due to colour variation during sexual repro-
duction.
This green colour passes to its offsprings. So that all its progeny are green.
Crows cannot identify the green beetles on grass.
But crows can feed the red beetles.
As a result there are more and more green beetles than red ones.
The variation of colour in beetle ‘green’ gave a survival advantage to green beetles than
red beetles. It is nothing but natural selection.
Mendelism :-
Gregor John Mendel was a monk in monastery in Austria.
In 1857 he started working on the problem of how variations were passed from one genera-
tion to the other.
He did experiments in the monastery garden.
Mendel had chosen garden pea as materials for his experiments because it has the follow-
ing reasons :-
1. Well defined characters 2. Bisexual flowers 3. Predominantly self fertilization
4. Early hybridization 5. It is a Annual plant
Mendel had chosen 7 pairs of contrasting characters for his study in pea plants. They are ...
1. Flower colour : Purple - White
2. Flower position : Axial - Terminal
3. Seed colour : Yellow - Green
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