Question

If the distance between five genes P, Q, R, S and T are 30 cM, 20 cM, 5 cM and 50 cM respectively, which two genes are likely to go along in the inheritance with the highest chance of co-occurrence?

• A. Gene P and Q
• B. Gene Q and R
• C. Gene S and T
• D. Gene R and S

Answer 1

The correct option is D Gene R and S

Linkage is the phenomenon of the physical association of genes on a chromosome. The linked genes do not show independent assortment rather they inherit as a group during gamete formation. Distance between the genes decides the strength of linkage; the higher is the distance lesser will be the strength and the shorter the distance stronger will be the linkage. The closer two genes are, the more likely they are to be inherited together (co-occurrence).

The physical distance between the genes is a measure in map units or recombination units. Centimorgan (cM) is the unit used for its measurement. A centimorgan is a unit of genetic distance that represents a 1% probability of recombination during meiosis.

In the question, the lowest frequency of recombination is 5 cM, which is in between gene R and S. so among all the genes P-Q, Q-R, R-S and S-T, gene R-S will go along in inheritance with the least chance of crossing over/recombination. Hence, they will have the highest probability of co-occurrence in the gamete.