What does the term phenotype ratio refer to in genetics?

The term phenotype ratio refers specifically to the ratio of different phenotypes observed in the offspring resulting from a genetic cross. This concept is crucial in genetics as it provides insight into how traits are expressed based on the genotype of the parents and the patterns of inheritance.

When a genetic cross is performed, especially one involving traits governed by simple dominance (such as Mendelian traits), the resulting offspring may exhibit a variety of observable traits, or phenotypes. For example, in a classic monohybrid cross, the phenotype ratio can often be simplified to typical 3:1 for dominant and recessive traits. This ratio allows scientists to predict the likelihood of certain traits appearing in future generations based on the genetic makeup of the organisms involved.

In contrast, the other choices refer to different concepts within genetics, such as allele frequency, reproductive output, and mutation rates, which do not specifically relate to the proportion of observable traits among offspring. The phenotype ratio is a critical tool in understanding the relationship between genotype and observable characteristics, making option C the correct choice here.