Question

There are three genes a, b and c. The percentage

of crossing over between a and b is 20%, b and c

is 28% and a and c is 8%. What is the sequence

of genes on chromosome?​

Answer 1

$\huge{\mathcal{\purple{A}\green{N}\pink{S}\blue{W}\purple{E}\green{R}\pink{!}}}$

$\huge\mathcal{\red{\underline{\purple{\boxed{\pink{B-A-C}}}}}}$

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.

$\huge{\mathcal{\purple{T}\green{H}\pink{A}\blue{N}\purple{K}\green{S}\pink{!}}}$