A dihybrid cross involves organisms that are heterozygous for two specific genes, indicated by the prefix "di-" meaning two. For example, consider a dihybrid genotype represented as RrYy, where "R" and "Y" are dominant alleles, and "r" and "y" are recessive alleles. In this case, the organism is heterozygous for both the shape gene (R for round and r for wrinkled) and the color gene (Y for yellow and y for green). This results in a phenotype of a round yellow pea, showcasing the dominant traits.
In genetic terms, the dominant allele masks the effect of the recessive allele. Therefore, in a dihybrid organism like RrYy, the presence of one dominant allele for each gene ensures the expression of the dominant traits. Understanding dihybrid crosses is essential for predicting the genetic variation in offspring when two heterozygous parents are crossed. This foundational knowledge sets the stage for exploring the outcomes of dihybrid crosses in future discussions.