Final answer:
The genotype of a round pea could be either homozygous (AA) or heterozygous (Aa). A test cross with a wrinkly pea plant (rr) resulting in all round pea offspring does not conclusively indicate the genotype of the round pea parent. If the round pea parent is heterozygous (Aa), the probability of all offspring being round is 27/64. The correct answer is option a.
Step-by-step explanation:
If for peas, a round shape is the dominant allele (A), and a wrinkly shape is the recessive allele (a), the genotype of a round pea could be either homozygous (AA) or heterozygous (Aa). Without additional information, such as the result of a test cross, we cannot determine the exact genotype. Only if we observe offspring with a wrinkly phenotype would we know that the round pea parent must have had a heterozygous genotype (Aa).
For the scenario presented in the question: Since all three offspring plants exhibit round peas after performing a test cross between a wrinkly pea plant (rr) and a plant of unknown genotype with round peas, we cannot definitively conclude whether the unknown parent was homozygous (AA) or heterozygous (Aa) dominant. However, if the parent with round peas was heterozygous (Aa), the probability of getting three round pea plants in the offspring would be (3/4)^3, or 27/64, since each offspring has a 3/4 chance of having the round phenotype.