Cross 1 shown in Figure 4.22 illustrates genetic complementation of flower-color mutants. The  produced from this cross of two pure-breeding mutant parental plants are dihybrid (CcPp) and have wild-type flower color. If these F₁ are allowed to self-fertilize, what phenotypes are expected in the F₂  and what are the expected ratios of the phenotypes?

Key Concepts

Genetic Complementation

Genetic complementation occurs when two different mutations in two parents can produce a wild-type phenotype in their offspring. This typically indicates that the mutations affect different genes or pathways. In the context of flower-color mutants, if the mutations are in different genes, the F₁ generation can express the wild-type phenotype due to the presence of at least one functional allele from each parent.

Dihybrid Cross

A dihybrid cross involves two traits, each represented by two alleles, leading to a combination of four possible gametes from each parent. In this case, the traits are flower color and another trait represented by the alleles C and P. The resulting F₁ generation (CcPp) can produce gametes that combine these alleles in various ways, which is essential for predicting the phenotypic ratios in the F₂ generation.

Phenotypic Ratios

Phenotypic ratios describe the relative frequencies of different phenotypes in the offspring resulting from a genetic cross. For a dihybrid cross of two heterozygous parents (CcPp x CcPp), the expected phenotypic ratio in the F₂ generation is typically 9:3:3:1, representing the combinations of dominant and recessive traits. Understanding this ratio is crucial for predicting the outcomes of the self-fertilization of the F₁ generation.