Question

You cross a plant that makes smooth peas with a plant that makes wrinkled peas (rr). If half of the offspring from that cross are smooth and half are wrinkled, what is the genotype of the smooth pea producing parent plant?

Answer 1

Rr

Step-by-step explanation:

This cross is a typical example of a test cross. A test cross is a cross between a heterozygous F1 progeny (different alleles) and a homozygous recessive parent in order to determine the actual genotype of the dominant parent i.e. whether homozygous or heterozygous dominance. In a test cross, if any of the offsprings show a recessive phenotype, it means the dominant parent is heterozygous

In this case, the allele for smooth pea (R) is dominant over that of wrinked pea (r).

If a cross between a smooth pea plant and a wrinkled pea plant gave rise to 50% phenotypical wrinkled pea plants (rr genotype, because the wrinkled shape can only express itself if it is in a homozygous state), it means that the smooth pea parent plant is heterozygous for pea shape (Rr) i.e. the allele for smooth shape was masking that of wrinkled shape in the smooth pea parent plant.