Product Method

The purpose is to estimate the recombination fraction between two linked loci with the greatest precision. The product method is one of several methods to estimate the percent recombination between linked loci. The advantage of the product method is that this method is the least affected by differences in viability among gametes with different genotypes.

Reference: Immer, F.R. 1930. Formulae and tables for calculating linkage intensities. Genetics 15:81-98.

Let us start with a segregating di-hybrid F families that contains the four phenotypes A_B_, A_bb, aaB_, and aabb. The observed relative frequencies of these classes are r, s, t, and u, respectively. If there is complete dominance at both loci we expect a 3:1 ratio for each gene considered seperately. We can then use the X test to determine whether the overall di-hybrid ratio deviates significantly from independent assortment between A and B. If there is a significant X for deviation from independence, then we can procede to determine the linkage intensity between the two loci using R.A. Fisher's product method. The formula is:

We mus solve for p which is the recombination faction. Table have been developed which solve for p, given that we have calculated the ru/st ratio. The same tables also provide the associated standard errors which determine the precision of the estimate of p. The tables provide information on F₂ coupling, F₂ repulsion, and testcross families.