Application of a recombination model in calculating the variance of sib pair genetic identity

Using a previously described model of crossing over (Risch & Lange, 1979), we have calculated analytically the variance in the proportion of genes identical by descent shared by two sibs. The prior distributions for numbers of chiasmata reported in Suarez et al. (1979) were used to calculate a standard deviation of 0.040 for the 22 human autosomes. It is also shown that any two identity by descent values within a sibship are uncorrelated.