Question

The recombination frequency (expressed as percentage) between X & Y is 4%, X & Z is 16%, Y & Z is 20%. Based on the recombination frequency, arrange the genes on the chromosome.

• A. XYZ
• B. XZY
• C. YZX
• D. YXZ

Answer 1

The correct option is D YXZ

Alleles of a particular gene are present at discrete loci on the chromosome. The distance between two gene loci on a chromosome is expressed in terms of a unit known as CentiMorgan (cM) or map unit (m.u).
Greater the distance between the genes, higher is the chance of crossing over between them, greater is the frequency of recombination.
Now, in this case, since the recombination percentage is given, hence, the relative distance between a pair of genes can be obtained by considering the fact that “greater the recombination frequency percentage, greater will be the distance between the two gene”.
Since the recombination frequency is highest between Y and Z, these two will be the farthest apart on the chromosome and X is located in between them.
Thus, the sequence becomes YXZ, represented as follows:-