The recombination frequency between three genes a, b, and c located on the same chromosome is obtained as follows:
a and c – 28%
a and b – 18%
b and c – 10%
based on the result, which two genes are closest to each other?

Genes B and C with 10% recombination frequency are closest to each other. Because recombination happens at random, the distance between genes that are farther from each other creates higher recombination frequency. A low recombination frequency of 10% means the genes are closest to each other. The short distance between the two genes allow fewer recombination to happen, thus the frequency is low.