Answer:
b, a, c
Step-by-step explanation:
Since recombination frequency is directly proportional to the distance between genes, the values are used to locate genes on a chromosome. Here three genes a, b and c can assume any of three linear sequences: a-b-c or a-c-b or b-a-c, which depends on the gene present in the middle. Here, recombination frequency for a and b (X) = 20%, that for a and c (Y) = 8% and for b and c (Z) =28%. As we can see that Z = X + Y or 28 = 20+8 which means that genes b and c are present at extremes and a is in the middle. Thus, the sequence of genes is b-a-c.