Question

How can the concept of recombination frequency be used in genetic mapping?

Answer 1

Recombination frequency (RF) is used to measure genetic linkage and in creating genetic linkge map because the frequency of a single chromosomal crossover between a pair of genes at the time of meiosis is called as RF. The unit in which distances are denoted are centrograns or map units (1% RF = 1 centrogran/ 1 map units). It helps in getting the approx distance between the two genes. In other words longer the recombination frequency more far are the pair of genes from each other and smaller the recombination frequency smaller is the distance between the pair of genes. Example : suppose there are 3 genes X, Y, Z and we need to know the order in which they are on the chromosome. (xyz or yxz or zxy). If we know the recombination frequency of all the three pairs of genes (xy,xz,yz) then it is easy to know which of the two genes lies at the furthest distance and which single gene lies in the middle. Let's assume the RF ( Recombination frequency)

1. Between X and Y = 13

2. Between Y and Z = 6

3. Between X and Z = 18

With this the genes which have the longest recombination frequency that is X and Z will be the genes which are furtherest genes from each other and the gene which is left that is Y will be the middle gene.

On the other part of we calculate the distance between X to Y and Y to Z is (13+6) = 19 whereas if we add the distance between X and Z is 18. This difference is due to double cross over on chromosome. Therefore we should measure RF for the closest genes which minimizes the double cross over and helps in getting accurate map distances.