Question

In a particular plant, two genes control leaf shape and fruit color. Round leaves (R) are dominant to jagged leaves (r). Yellow fruits (Y) are dominant to white fruits (y). A true-breeding round-leaved, yellow-fruited plant is crossed with a jagged-leaved, white-fruited plant. What are the genotypes of the parent plants involved in this cross?

• A. RRYY x RRYY
• B. RRYY x rryy
• C. RrYy x RrYy
• D. RrYy x rryy

Answer 1

The correct option is B RRYY x rryy

A true breeding plant is obtained by continuous self pollination which shows stable inheritance and expression of certain traits for several generations. It is also known as pure line breeds.
True breeding plants are homozygous. Thus the genotype would have identical alleles for a character.
In the question given above the plant differs in two characters- shape of the leaf and colour of the fruit. It is an example of a dihybrid cross.
According to the question, round leaves (R) are dominant to jagged leaves (r), and yellow fruits (Y) are dominant to white fruits (y).
Therefore, pure round leaved and yellow fruited plants would be represented as RRYY (homozygous dominant for both the genes) and pure jagged leaved and white fruited plants would be represented as rryy (recessive for both the genes).
Thus, the genotypes of the parent plants involved in this cross are RRYY X rryy.