AP Syllabus focus:
‘Dihybrid crosses analyze inheritance of two genes simultaneously, illustrating independent assortment and expected phenotypic ratios.’
Dihybrid crosses extend single-gene genetics to track two traits at once. They help you connect allele segregation during meiosis to predictable offspring patterns when genes assort independently.
Core idea: tracking two genes at once
A dihybrid cross follows the inheritance of two different genes (often written as and ) through gametes and offspring. It is most informative when the parental generation produces heterozygous individuals for both genes (e.g., ), because multiple allele combinations are possible.
Key term
Practice Questions
FAQ
Because each gamete gets one allele from each gene, and the two genes can pair in all combinations under independent assortment.
If the genes assort independently and dominance rules are simple, you can treat outcomes as combinations of two single-gene patterns.
Phenotypes may split into three classes for that gene, increasing the total number of combined phenotype categories in the dihybrid outcome.
Random sampling effects are stronger with small offspring numbers, so chance can skew observed counts away from expected proportions.
It means grouping multiple genotypes that produce the same visible trait (due to dominance) into a single phenotypic category before counting ratios.
