MULTIPOINT LINKAGE MAP OF THE HUMAN PSEUDOAUTOSOMAL REGION, BASED ON SINGLE-SPERM TYPING - DO DOUBLE CROSSOVERS OCCUR DURING MALE MEIOSIS

Sperm typing was used to measure recombination fractions among pseudoa utosomal markers and the beginning of the X/Y-specific sequences locat ed at the pseudoautosomal boundary. These experiments included primer- extension preamplification and PCR followed by allele typing using gel electrophoresis. A newly developed data-analysis program allowed the construction of the first multipoint-linkage sperm-typing map, using r esults obtained on seven loci from three individuals. The large sample size not only confirmed the increased recombination activity of the p seudoautosomal region but allowed an estimate of interference of recom bination to be made. The coefficient of coincidence was calculated to be .26 over a physical distance of only similar to 1,800 kb. The obser vation of a few sperm presumably resulting from double recombination a rgues that more than one crossover event can occur in this region duri ng male meiosis.