Question

A homozygous inflated pod shaped variety of pea plant (I) is crossed with a constricted variety of pea plant
(i) Answer the question that follows: Give the phenotypic ratio and the genotypic ratio of the offspring of the ${ F }_{ 2 }$ generations when the two hybrids of the ${ F }_{ 1 }$ generation are crossed.

Answer 1

For pod shape in pea plant inflated pod shape is a dominant trait whereas constricted pod shape is a recessive trait.

Complete answer:
Let P be the inflated pod shape and p be the constricted pod shape.
- The phenotypic ratio of the offspring of the ${ F }_{ 2 }$ generations when the two hybrids of the ${ F }_{ 1 }$ generation are crossed will be 3:1 and the genotypic ratio will be 1:2:1.
- When the homozygous plants of both the traits are crossed i.e. PPpp the resulting offspring will be Pp in the ${ F }_{ 1 }$ generation.
- progeny in the F1 generation are all having inflated pod shape which is the dominant trait even in the heterozygous condition.
- When two hybrids of the ${ F }_{ 1 }$ generation are crossed then the progeny in the ${ F }_{ 2 }$ generation is produced in a phenotypic ratio of 3:1 where 3 individuals are showing dominant traits and 1 individual is showing recessive traits.
- The genotypic ratio is 1:2:1, as there is one homozygous individual for each dominant and recessive trait whereas two individuals for the heterozygous dominant trait.
${ F }_{ 2 }$ generation

| P| p
---|---|---
P| PP| Pp
p| Pp| pp

Note:
- A dominant trait is expressed in both heterozygous and homozygous conditions. However, the recessive trait is expressed only in recessive conditions.
- Mendel’s law of dominance is as follows:
For every trait, 2 factors or alleles are passed down from parent to the children but only one of the two factors is expressed and the other one is not expressed. The factor that is expressed is dominant and the one that is not expressed is the recessive trait.