Question: 176: The recombination frequency between the genes \mathrm{a} \& \mathrm{c} is 5 \%, \mathrm{~b} \& \mathrm{c} is 15 \%, \mathrm{~b} \& \mathrm{~d} is 9 \%, \mathrm{a} \& \mathrm{~b} is 20 \%, \mathrm{c} & d is 24 \% and a & d is 29 \%. What will be the sequence of these genes on a linear chromosome?
(1) a, b, c, d
(2) a, c, b, d
(3) a, d, b, c
(4) d, b, a, c
Answer: Option (2)
Explanation:
Recombination frequency is directly proportional to the distance between genes on a chromosome.
The smallest recombination frequency is between \mathrm{a} \& \mathrm{c},
which is 5 \%, indicating that genes \mathrm{a} and
\mathrm{c} are closest to each other.
The recombination frequency between \mathrm{b} \& \mathrm{c} is 15 \%,
which is greater than 5 \% but less than that of \mathrm{a} \& \mathrm{b},
which is 20 \%.
This indicates that gene \mathrm{c} lies between \mathrm{a} and
\mathrm{b} on the chromosome.
The recombination frequency between \mathrm{b} \& \mathrm{d} is 9 \%,
showing that genes \mathrm{b} and \mathrm{d} are relatively close.
The largest recombination frequency is between \mathrm{a} \& \mathrm{d},
which is 29 \%, indicating that these genes are farthest apart.
Combining all the given distances, the correct linear order of genes is
a \rightarrow c \rightarrow b \rightarrow d.
Hence, option (2) is the correct sequence.