Final answer:
In a monohybrid test cross, the offspring can either be homozygous dominant (AA) or homozygous recessive (aa), indicating the correct answer is D) A and C. A test cross helps determine the genotype of an individual expressing the dominant trait by crossing it with a homozygous recessive individual.
Step-by-step explanation:
The offspring of a monohybrid test cross would show genotypes of either homozygous dominant or homozygous recessive. A test cross involves crossing an individual expressing a dominant trait with an individual that is homozygous recessive for that trait. This is done to determine the genotype of the dominant-expressing parent: whether it is a homozygote (AA) or a heterozygote (Aa).
In this cross, if the dominant-expressing parent is a homozygote (AA), all offspring will have the genotype AA (homozygous dominant). If the dominant-expressing parent is a heterozygote (Aa), the offspring will have genotypes of either Aa (heterozygous) or aa (homozygous recessive). Thus, the correct answer to the question is D) A and C because the genotypes that can be observed in the offspring of a monohybrid test cross could include both homozygous dominant (AA) and homozygous recessive (aa).
Moreover, a recessive trait will be observed in individuals that are homozygous for that trait (option c), meaning they have two recessive alleles (aa).
Understanding monohybrid cross results led Mendel to conclude that each parent contributes one of two paired unit factors to each offspring, resulting in a characteristic 3:1 phenotypic ratio in the F2 generation of a monohybrid cross. The F1 generation offspring are always heterozygous when true-breeding parents with contrasting traits are crossed.