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.

12/16 white : 3/16 green : 1/16 yellow

Key Concepts

Dihybrid Cross

A dihybrid cross involves two traits, each represented by two alleles, allowing the study of inheritance patterns for two genes simultaneously. In this case, the genes R and T are being analyzed for their interactions in producing different phenotypes. The F₂ generation results from crossing F₁ hybrids, revealing phenotypic ratios that reflect the combinations of alleles inherited from the parents.

Epistasis

Epistasis occurs when the expression of one gene is affected by another gene, leading to modified phenotypic ratios. In the context of the question, the dominant alleles R and T may interact in such a way that they influence pigment production differently, resulting in the observed ratios of white, green, and yellow phenotypes. Understanding this interaction is crucial for designing pathways that explain the F₂ ratios.

Phenotypic Ratios

Phenotypic ratios represent the relative frequencies of different phenotypes in the offspring of a genetic cross. The specified ratios of 12/16 white, 3/16 green, and 1/16 yellow indicate how the combinations of alleles from the R and T genes lead to varying expressions of pigment. Analyzing these ratios helps in constructing hypothetical pathways that account for the observed outcomes based on the genetic interactions.