Question

How can we find out about the allelic composition of a pea plant for the trait -yellow coloured pods?

• A. By performing a reciprocal cross
• B. By performing a back cross
• C. By performing a test cross
• D. No requirement for any kind of cross

Answer 1

The correct option is D No requirement for any kind of cross

Among all the characters shown by the pea plant, Mendel chose 7 characters for his study. The selection was done on the basis of distinct variants (traits) available for the characters. All these 7 characters had two traits each- one dominant and the other recessive. They are mentioned in a table given below.
The dominant trait is able to express itself in both homozygous (identical alleles are present), and heterozygous (both alleles are non-identical) conditions. But the recessive trait is only able to express itself in homozygous condition. This means if a plant is expressing a recessive trait, it is in a homozygous condition for that trait. From the table we can see that the yellow colour of pods is a recessive trait. So, there is no need for any cross to find out the allele composition of the plant. It is in homozygous condition.
Test cross is done to find out the allele composition of a plant which is expressing a dominant trait by crossing it with a homozygous recessive plant for the same character.
Back cross is crossing the $F_1$ progeny with any one of its parents.
A reciprocal cross is done by switching the traits of the parents.