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.
•He used all available techniques to avoid cross pollination by undesirable pollen
grains.
•He applied mathematics and statistics to analyse the results obtained by him.
, •Mendel selected 7 contrasting characters of garden pea for his hybridization
experiments.
Contrasting Characters Studied by Mendel in Pea
Characters Contrasting characters
( Dominant/Recessive
Stem height Tall/Dwarf
Flower colour Violet/White
Flower position Axial/Terminal
Pod shape Inflated/Constricted
Pod colour Green/Yellow
Seed shape Round/Wrinkled
Seed colour Yellow/Green
•Mendel conducted artificial hybridization/cross pollination using true breeding pea
lines. True breeding lines are those that undergo continuous self-pollination and
shows stable trait inheritance.
•Hybridization experiment includes emasculation (removal of anther) and transfer of
pollen (pollination).
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.
•He used all available techniques to avoid cross pollination by undesirable pollen
grains.
•He applied mathematics and statistics to analyse the results obtained by him.
, •Mendel selected 7 contrasting characters of garden pea for his hybridization
experiments.
Contrasting Characters Studied by Mendel in Pea
Characters Contrasting characters
( Dominant/Recessive
Stem height Tall/Dwarf
Flower colour Violet/White
Flower position Axial/Terminal
Pod shape Inflated/Constricted
Pod colour Green/Yellow
Seed shape Round/Wrinkled
Seed colour Yellow/Green
•Mendel conducted artificial hybridization/cross pollination using true breeding pea
lines. True breeding lines are those that undergo continuous self-pollination and
shows stable trait inheritance.
•Hybridization experiment includes emasculation (removal of anther) and transfer of
pollen (pollination).
