Final answer:
Genes A and B are farther apart on the chromosome than genes B and C as indicated by their recombination frequencies of 20% and 30%, respectively. This suggests a higher likelihood of crossovers occurring between genes that are more distant from each other.
Step-by-step explanation:
Recombination frequencies correlate with the genetic distance between two genes. The statement that recombinant offspring are recovered 20% of the time from single crossovers for genes A and B, and 30% for genes B and C, suggests that genes A and B are farther apart than genes B and C on the chromosome. Recombination between genes that are farther apart, like A and B, is more frequent because a crossover is more likely to occur between them.
Furthermore, recombination frequency can be used to create a genetic map of a chromosome where 1% recombination frequency equals 1 centimorgan (cM). A recombination frequency of 20% implies that genes A and B are 20 cM apart, while a frequency of 30% for genes B and C indicates they are 30 cM apart. When frequencies are between 0% and 50%, it indicates that the genes are linked on the same chromosome and crossing over can occur.