What is the expected phenotypic ratio in a monohybrid cross?

In a monohybrid cross, where two organisms heterozygous for a single trait are mated (for example, one parent with alleles Aa and the other also with Aa), the expected phenotypic ratio of the offspring is indeed 3:1. This ratio arises from the combination of alleles during gamete formation and fertilization as described by Mendel’s laws of inheritance.

In this scenario, there are three situations in which the offspring will display the dominant phenotype (AA or Aa) and only one situation where the offspring will express the recessive phenotype (aa). Therefore, when you count the possible phenotypes of the offspring, three out of four display the dominant trait, while one displays the recessive trait, thus yielding the 3:1 ratio.

This ratio showcases the prevalence of the dominant trait in the offspring when examining a single gene trait, making it a foundational concept in genetics.