Consider two hypothetical recessive autosomal genes a and b, where a heterozygot
ID: 25937 • Letter: C
Question
Consider two hypothetical recessive autosomal genes a and b, where a heterozygote is testcrossed to a double-homozygous mutant. Predict the phenotypic ratios under the following conditions. For parts B, C, and D the mutations are in cis.Part A: a and b are located on separate autosomes.
Part B: a and b are linked on the same autosome, but are so far apart that a crossover always occurs between them.
Part C: a and b are linked on the same autosome, but are so close together that a crossover almost never occurs.
Part D: a and b are linked on the same autosome about 10 mu apart.
Explanation / Answer
Consider two hypothetical recessive autosomal genes a and b, where a heterozygote is testcrossed to a double-homozygous mutant. Predict the phenotypic ratios under the following conditions. For parts B, C, and D the mutations are in cis.
Part A: a and b are located on separate autosomes.
1:1:1:1:
Part B: a and b are linked on the same autosome, but are so far apart that a crossover always occurs between them.
9:3:3:1:
Part C: a and b are linked on the same autosome, but are so close together that a crossover almost never occurs.
1:1:1:1:
Part D: a and b are linked on the same autosome about 10 mu apart.
AaBb 40%, Aabb 10%, aaBb 10%, aabb 40%