Question

A pea plant bearing violet flowers, pure line for the trait, was crossed with another plant bearing white flowers. The $F_1$ progeny was self-crossed. If 200 plants are produced in $F_2$ generation, predict the number of plants under each category mentioned:
i. Dominant
ii. Recessive
iii. Homozygous dominant

• A. i-50, ii-100, iii-50
• B. i-150, ii-50, iii-50
• C. i-100, ii-50, iii-50
• D. i-50, ii-50, iii-100

Answer 1

The correct option is B i-150, ii-50, iii-50

In pea plants, violet colour of flowers is dominant over white.
Let the allele for violet colour be 'P' and the allele for white colour be 'p'.

The genotype of the pea plant producing violet flowers is PP (as it is a pure line)

The genotype of the pea plant producing white flowers is pp.

When these plants are crossed, all the $F_1$ hybrids produce flowers of violet colour (Pp).

On selfing the $F_1$ hybrid, $F_2$ generation was obtained.



Genotypic ratio in $F_2$ generation: PP : Pp : pp = 1 : 2 : 1

Phenotypic ratio in $F_2$ generation: Plants producing violet flowers: Plants producing white flowers = 3 : 1

i) Out of 4 plants, no. of plants dominant for the flower colour trait = 3 (1 PP, 2 Pp)
$\Rightarrow$ Out of 200 plants, no. of plants dominant for the flower colour trait $=\left(\frac{3}{4}\right)\times 200=150$

ii) Out of 4 plants, no. of plants recessive for the flower colour trait = 1 (pp)
$\Rightarrow$ Out of 200 plants, no. of plants recessive for the flower colour trait $=\left(\frac{1}{4}\right)\times 200=50$

iii) Out of 4 plants, no. of homozygous dominant plants for the flower colour trait = 1 (PP)
$\Rightarrow$ Out of 200 plants, no. of homozygous dominant plants for the flower colour trait $=\left(\frac{1}{4}\right)\times 200=50$