While evidence exists for the presence of positive crossover interference in humans, little work has been done to measure the strength of this interference. Investigations of interference in experimental organisms, such as Drosophila and mice, have used the observed frequencies of rare multiple recombination events in sets of adjacent intervals. Such an approach requires many thousands of meioses, each informative for the same set of markers, a resource which is not readily available in humans.
We recently constructed new comprehensive human genetic maps, based upon nearly one million genotypes from eight CEPH families and incorporating over 8,000 STRP markers from several laboratories. These data are the best available resource to date for the study of interference in humans; they not only provide evidence for the presence of interference genome-wide, but also allow a characterization of the extent of human crossover interference and the derivation of an empirical map function.
Using these data, the number and locations of the recombination events on each chromosome may be estimated. The difference between the distribution of the number of recombination events per chromosome and that expected under no interference provides strong evidence for the presence of positive crossover interference in humans. In order to further characterize the strength of interference, we estimate the distribution of distances between recombination events, either by fitting a gamma renewal model or by using logspline density estimation (a nonparametric approach). Initial analysis of these data suggests that an appropriate map function for humans is between the Haldane and Kosambi map functions.