Question

Two pea plants are crossed to make 1,000 offspring. All offspring possess long pods and round peas. Long pods (L) are dominant to short pods (l), and round peas are dominant (R) to wrinkled peas (r). Which of the following are possible genotypes of the parent plants?

Answer 1

Answer:

Parental Genotypes: LLRR and llrr or LLRR and LLRR respectively

Explanation:

This cross is a dihybrid cross involving two genes; one coding for pod length and the other for pea shape.

Gene L represents the pod length while gene R represents the pea shape. According to the question, allele for long pods (L) is dominant over allele for short pods (l) in the first gene while the allele for round peas (R) is dominant over the allele for wrinkled peas (r) in the second gene.

According to the question, all 1000 offsprings possess long pods and round peas, meaning that all offsprings were dominant for both traits (pod length and pea shape).

A dominant plant can either be homozygous or heterozygous depending on whether the pair of alleles are the same or different respectively. Hence, The offsprings will only be dominant for both traits in a homozygous (LLRR) or heterozygous (LlRr) state.

These two offspring genotypes (LLRR and LlRr) are possible if the genotype of the parents are:

1) Both homozygous dominant i.e LLRR. In this case, all offsprings will possess long pods and round peas (dominant traits)

2) Each parent is purebred i.e. homozygous dominant (LLRR) and homozygous recessive (llrr) respectively. In this case, all F1 offsprings will be heterozygous dominant (LlRr), hence, possess long pods and round peas.