Page 1 - Lesson Notes- Principle of inheritance & Variation
P. 1
CBSE Class 12 Biology
Revision Notes
CHAPTER- 05
PRINCIPLES OF INHERITANCE AND VARIATION
Genetics is the study of principles and mechanism of heredity and variation. Gregor Johann
Mendel is known as ‘father of Genetics’.
Inheritance is the process by which characters are passed on from parent to progeny. It
is the basis of heredity.
Variation is the degree by which progeny differ from their parents. Variation may be in
terms of morphology, physiology, cytology and behavioristic traits of individual
belonging to same species.
Variation arise due to
Reshuffling of gene/chromosomes.
Crossing over or recombination
Mutation and effect of environment.
Mendel’s Law of Inheritance : Mendel conducted hybridization experiments on garden pea
(Pisum sativum) for seven years and proposed the law of inheritance in living organisms.
Selection of pea plant: The main reasons for adopting garden pea (Pisum sativum) for
experiments by Mendel were –
Pea has many distinct contrasting characters.
Life span of pea plant is short.
Flowers show self pollination, reproductive whorls being enclosed by corolla.
It is easy to artificially cross pollinate the pea flowers. The hybrids thus produced
were fertile.
Working method: Mendel’s success was also due to his meticulous planning and method of
work –
He studied only one character at a time.
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