Question

A cross is made between true breeding lines of pea plants with axillary (A) and terminal (a) flowers. What is the ratio between the number of possible genotypes of homozygous and heterozygous plants in ${\text{F}}_2$ progeny?

• A. 3:1
• B. 1:2:1
• C. 1:1
• D. 1:1:2

Answer 1

The correct option is C

1:1

Genotype of parent plant with axillary flower: AA
Genotype of parent plant with terminal flower: aa

${\text{F}}_1$ : AA X aa
${\text{F}}_1$ generation produces only heterozygous (Aa) offsprings.

${\text{F}}_2$ : Aa X Aa
Out of possible ${\text{F}}_2$ progenies in monohybrid cross:

• ${\frac{1}{4}}^{th}$ are homozygous dominant (AA).
• $\frac{1}{2}$ are heterozygous dominant(Aa).
• ${\frac{1}{4}}^{th}$ are homozygous recessive (aa).

Thus, the fraction of homozygous progeny is $\frac{1}{4}$ + $\frac{1}{4}$ = $\frac{1}{2}$, while the fraction of heterozygous being $\frac{1}{2}$ .
Therefore, the ratio between all the homozygous and heterozygous plants is:
$\frac{1}{2}$ : $\frac{1}{2}$ = 1:1