In a cross between AABB × aabb, the ratio of F2 genotypes between AABB, AaBB, Aabb and aabb would be:
Correct answer: C. 1 : 2 : 2 : 1
- A. 9 : 3 : 3 : 1
- B. 2 : 1 : 1 : 2
- C. 1 : 2 : 2 : 1
- D. 7 : 5 : 3 : 1
Explanation
In a cross between AABB × aabb, each parent can only produce one type of gamete: AB from AABB and ab from aabb. When these are crossed, the F1 generation is uniformly AaBb. When the F1 individuals are self-crossed (AaBb × AaBb), the F2 generation will segregate according to Mendelian principles, producing a 1:2:2:1 ratio of genotypes (AABB, AaBB, Aabb, aabb). This is because the alleles segregate independently, and each combination has a distinct probability of occurring. The other options represent incorrect ratios that do not apply to this genetic cross.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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