Final answer:
A testcross of an individual with a genotype AaBb will result in 25% of the progeny having purple flowers, as both dominant alleles A and B are required to produce the purple flower phenotype in pea plants.
Step-by-step explanation:
The question deals with the inheritance of flower color in pea plants, which is a genetics concept in biology. To determine the proportion of progeny with purple flowers after a testcross of an individual with a genotype of AaBb, a Punnett square analysis is useful. Since the flower color is determined by two genes (A and B), both of which require at least one dominant allele to produce a purple flower, the genotype of AaBb gives rise to a ratio where three out of four combinations have at least one dominant allele for both genes. This results in a 3:1 phenotype ratio, where 75% (or 3/4) of the progeny will have purple flowers and 25% (or 1/4) will have white flowers.
Using the information provided, if we conduct a testcross (AaBb x aabb), each of the genes will independently assort to give four different gametes from the AaBb parent: AB, Ab, aB, and ab. Because a testcross involves crossing with a homozygous recessive individual (aabb), all the gametes from this parent will be ab. Therefore, the expected outcome for the progeny will be 1/4 AaBb (purple), 1/4 Aabb (white), 1/4 aaBb (white), and 1/4 aabb (white), resulting in a ratio where 25% of the progeny will have purple flowers.