Mendelian Inheritance Dihybrid Cross Ratios
Dihybrid cross flashcards cover the 9:3:3:1 phenotypic ratio and its modifications for students in AP Biology, genetics courses, and MCAT prep. Mastering these ratios builds the foundation for understanding independent assortment, epistasis, and how multiple gene loci interact to produce observable traits.
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5 CardsEpistasis effect on 9:3:3:1 ratio
How many gamete types does AaBb produce?
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What is the difference between monohybrid and dihybrid crosses?
A monohybrid cross involves one gene locus (3:1 ratio), while a dihybrid cross involves two gene loci (9:3:3:1 ratio). Dihybrid crosses demonstrate independent assortment between two traits simultaneously.
- Monohybrid: Aa × Aa → 3:1
- Dihybrid: AaBb × AaBb → 9:3:3:1
Why does the dihybrid ratio become 9:7 in some crosses?
A 9:7 ratio occurs with complementary epistasis, where both dominant alleles must be present for a trait to appear. If either locus is homozygous recessive, the trait is suppressed, collapsing the normal 9:3:3:1 into 9:7.
How do I set up a dihybrid Punnett square?
List all 4 gamete types from each parent (AB, Ab, aB, ab) as row and column headers, creating a 4×4 grid of 16 boxes. Fill each box by combining the gametes, then count phenotype classes to verify the 9:3:3:1 ratio.