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.