Two genes interact to produce various phenotypic ratios among F₂ progeny of a dihybrid cross. Design a different pathway explaining each of the F₂ ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F₂ progeny produced by crossing wild-type F₁ organisms with the genotype RrTt.

13/16 white : 3/16 green

Key Concepts

Dihybrid Cross

A dihybrid cross involves two traits, each controlled by different genes, typically represented by two pairs of alleles. In this scenario, the genes R and T are being studied, where each gene can have a dominant or recessive allele. The phenotypic ratios observed in the offspring result from the independent assortment of these alleles during gamete formation, leading to various combinations in the F₂ generation.

Phenotypic Ratios

Phenotypic ratios describe the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. In this case, the ratio of 13/16 white to 3/16 green indicates that the majority of the F₂ progeny exhibit a white phenotype, while a smaller proportion shows green. Understanding how these ratios arise from the interactions of alleles is crucial for explaining the genetic pathways involved.

Gene Interaction

Gene interaction occurs when the effects of one gene are modified by one or more other genes, leading to a combined effect on the phenotype. In this question, the dominant alleles of genes R and T catalyze different reactions that contribute to pigment production. The recessive alleles are null, meaning they do not produce functional proteins, which is essential for understanding how the presence or absence of these alleles influences the resulting phenotypes.