Question

In a cross between plants with purple flowers and plants with white flowers, the F1 had all
purple flowers. When F1 generation was self- bred, the F2 generation gave rise to 100
individuals, 75 of which had purple flowers. Make a cross and answer.
(a) What are the genotypes of F1 individual?
(b) What is the ratio of purple flowered plants in F2 generation?
(c)Represent F2 generation in Punnette’s Checker square.

Answer 1

a) Genotypes of F1 individuals: Aa

b) Ratio of purple : white = 3 : 1.

Explanation:

Only purple flowers are seen in the F1 generation. That implies that the purple colour (A allele) is dominant over the white colour (a allele).

In that case the genotype in parent generation,

Parent with purple flower AA

Parent with white flower aa.

So the genotype of all the flowers in F1 generation is Aa.

In the F2 generation,

The genotype of both the parents = Aa

In F2 generation total of 100 offspring, out of which 75 are purple means 25 are white.

Ratio of purple:white flowers = $\frac{75}{25} = \frac{3}{1}$

Ratio of purple : white = 3 : 1.