Genetic Map Functions

Abstract

A genetic map function gives a relation r = M(d) connecting recombination fractions r and genetic map distances d between pairs of loci along a chromosome. They have been widely used in genetics because (a) genetic map distances are additive, whereas recombination fractions are not; and (b) recombination fractions are much easier to estimate from data. In effect, map functions correct for multiple exchanges in chromosomal intervals during meiosis. The most well-known map function is that due to Haldane, r = 0.5(1 − exp(−2d)), which arises in the Poisson or no- interference model for recombination. Another is associated with the name Kosambi. In general, map functions should be regarded as organism specific, as they embody certain assumptions about recombination, in particular, the nature and extent of genetical interference. However, map functions only consider pairs of loci, and do not necessarily correspond to global models of recombination. While genetical interference has some consequences for map functions, it is not well captured by the associated map function. When multilocus mapping is carried out with a full probability model for recombination, map functions are not needed.