Dihybrid Cross Practice Flashcards

Dihybrid Cross Ratios

• Phenotypic ratio for a cross between two heterozygous individuals (Aa x Aa) is 3:1, indicating three dominant expressions to one recessive.
• Genotypic ratio for the same cross (Aa x Aa) is 1:2:1, showing one homozygous dominant, two heterozygous, and one homozygous recessive genotype.

Monohybrid Cross Ratios

• When crossing a heterozygous individual (Aa) with a homozygous recessive individual (aa), both the phenotypic and genotypic ratio result in 1:1, indicating equal chances of dominant and recessive traits appearing.

Dihybrid Cross Ratios with Two Traits

• In a dihybrid cross between two individuals heterozygous for both traits (AaBb x AaBb), the phenotypic ratio is 9:3:3:1. This reflects the combinations of traits for two independent genes.
• When crossing one individual heterozygous for both traits (AaBb) with one homozygous recessive individual (aabb), the resulting phenotypic and genotypic ratio is 1:1:1:1, indicating equal distribution of the four possible genotype combinations.

Identification of Dominant Traits in Pedigrees

• In pedigree charts, a dominant trait can be identified by observing that every affected individual has at least one affected parent.
• The trait tends to appear in every generation once it is present, suggesting a direct inheritance pattern.