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Get Answers to all your Questions
(a) Why did Mendel carry out an experiment to study inheritance of two traits in garden pea?
(b) What were his findings with respect to inheritance of traits in F1 and F2 generation?
(C) State the ratio obtained in the F2 generation in the above mentioned experiment. Explain with the help of a cross.
Answers (1)
(a)
Mendel performed experiments involving two traits (dihybrid cross) to find out whether different traits are inherited together or independently of each other.
He wanted to understand the inheritance pattern when more than one character is considered at the same time.
(b)
F1 Generation:
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When Mendel crossed plants differing in two pairs of contrasting traits, all F1 plants showed only the dominant traits.
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Example: All plants had round and yellow seeds.
F2 Generation:
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In the F2 generation, both parental and new combinations of traits appeared.
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This showed that the inheritance of one trait is independent of the inheritance of the other trait.
This observation led to the Law of Independent Assortment.
(c)
F2 Phenotypic Ratio - 9:3:3:1
Let us consider:
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Seed shape:
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Round (R) – dominant
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Wrinkled (r) – recessive
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Seed colour:
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Yellow (Y) – dominant
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Green (y) – recessive
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Parental generation:
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RRYY (Round, Yellow) × rryy (Wrinkled, Green)
F1 generation:
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All plants are RrYy (Round, Yellow)
F2 generation:
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Cross: RrYy × RrYy
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Gametes produced: RY, Ry, rY, ry
RY Ry rY ry
--------------------------------
RY | RRYY RRYy RrYY RrYy
Ry | RRYy RRyy RrYy Rryy
rY | RrYY RrYy rrYY rrYy
ry | RrYy Rryy rrYy rryy
The combination of these gametes gives the following phenotypes:
| Phenotype | Number |
|---|---|
| Round Yellow | 9 |
| Round Green | 3 |
| Wrinkled Yellow | 3 |
| Wrinkled Green | 1 |
The 9 : 3 : 3 : 1 ratio in the F2 generation proves that the traits assort independently during gamete formation.
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