Following two genes
A dihybrid cross follows the inheritance of two genes at the same time. This produces more possible gamete, genotype and phenotype combinations than a monohybrid cross.
For example, consider two genes controlling seed characteristics:
- R produces round seeds and r produces wrinkled seeds.
- G produces yellow seeds and g produces green seeds.
An individual heterozygous for both genes has the genotype RrGg.
Writing dihybrid genotypes
When writing a genotype involving two genes, keep the two alleles of one gene together and then write the two alleles of the second gene.
| Notation | Meaning |
|---|---|
| RrGg | Heterozygous for both genes |
| RRGg | Homozygous for R/r and heterozygous for G/g |
| rrgg | Homozygous recessive for both genes |
Writing a genotype as RrGg, rather than mixing alleles from different genes together, makes it clear which two alleles belong to each gene.