Final answer:
In test crosses (option C), the expected ratios among the offspring can either be 1:1 or 1:1:1:1, depending on whether the cross is a monohybrid or dihybrid test cross used to determine the genotype of an individual with the dominant phenotype.
Step-by-step explanation:
The two different kinds of ratios among the offspring, either 1:1 or 1:1:1:1, can be expected in test crosses (C). In a monohybrid cross, such as a cross between true-breeding pea plants with yellow seeds (YY) and green seeds (yy), we typically expect all offspring to have the dominant phenotype if one parent is homozygous dominant and the other is homozygous recessive, resulting in a uniform 1:0 phenotypic ratio in the F1 generation. In contrast, a dihybrid cross, involving two traits, generally yields a 9:3:3:1 phenotypic ratio in the F2 generation if the two genes assort independently.
However, in a test cross, which is used to determine the genotype of an individual with a dominant phenotype by crossing it with a homozygous recessive individual, the possible ratios are either 1:1 (if the dominant phenotype parent is heterozygous) or all offspring displaying the dominant phenotype (if the dominant phenotype parent is homozygous dominant).
A test cross could also result in a 1:1:1:1 ratio if we're considering a dihybrid test cross (two genes, each with heterozygous and homozygous recessive possibilities) which will result in an equal mix of the four possible genotypes regarding the two traits.