Questions and Answers
What is the phenotypic ratio for Aa x Aa (two heterozygous)?
3:1
What is the genotypic ratio for Aa x Aa (two heterozygous)?
1:2:1
What is the phenotypic and genotypic ratio for Aa x aa (1 heterozygous and 1 homozygous)?
1:1
What is the phenotypic ratio for AaBb x AaBb (two pairs of heterozygous cross)?
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What is the phenotypic and genotypic ratio for AaBb x aabb (1 pair heterozygous and 1 homozygous)?
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How can you identify a dominant trait from a pedigree chart?
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Study Notes
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.
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Description
Test your knowledge of phenotypic and genotypic ratios with these flashcards on dihybrid crosses. Each card presents scenarios using various genetic combinations, allowing for a comprehensive review. Perfect for students studying genetics and Mendelian inheritance.