DNA PROFILE MATCH PROBABILITIES IN A SUBDIVIDED POPULATION - WHEN CANSUBDIVISION BE IGNORED

Li and Chakravarti [Li, C. C. & Chakravarti, A. (1994) Hum. Hered. 44, 100-109] compared the probability (M(0)) of a random match between th e two DNA profiles of a pair of individuals drawn from a random-mating population to the probability (M(F)) Of the match between a pair of r andom individuals drawn from a subdivided population, The level of het erogeneity in this subdivided population is measured by the parameter F, where there is no subdivision when F = 0 and increasing values off indicate increasing subdivision. Li and Chakravarti concluded that it is conservative to use the match probability M(0), which is derived un der the assumption that the two individuals are drawn from a homogeneo us randommating population without subdivision. However, M(0) may not be always greater than M(F), even for biologically reasonable values o ff. We explore here those mathematical conditions under which M(0) is less than M(F), and we find that Mo is not conservative mainly when th ere is an allele with a much higher frequency than all the other allel es. When empirical data for both variable number of tandem repeat (VNT R) and short tandem repeat (STR) systems are evaluated, we find that i n the majority of cases M(0) represents a conservative probability of a match, and so the subdivision of human populations may usually be ig nored for a random match, although not, of course, for relatives. Loci for which M(0) is not conservative should be avoided for forensic inf erence.