Recombination, together with mutation, gives rise to genetic variation in populations. Here we leverage the recent mixture of people of African and European ancestry in the Americas to build a genetic map measuring the probability of crossing over at each position in the genome, based on about 2.1 million crossovers in 30,000 unrelated African Americans. At intervals of more than three megabases it is nearly identical to a map built in Europeans. At finer scales it differs significantly, and we identify about 2,500 recombination hotspots that are active in people of West African ancestry but nearly inactive in Europeans. The probability of a crossover at these hotspots is almost fully controlled by the alleles an individual carries at PRDM9 (Pvalue < 10~(-245)). We identify a 17-base-pair DNA sequence motif that is enriched in these hotspots, and is an excellent match to the predicted binding target of PRDM9 alleles common in West Africans and rare in Europeans. Sites of this motif are predicted to be risk loci for disease-causing genomic rearrangements in individuals carrying these alleles. More generally, this map provides a resource for research in human genetic variation and evolution.%基因图度量一个基因组中每个点上发生交叉的rn概率，是研究不同人种之间差异情况的重要工rn具。现在，研究人员利用来自18，000名非洲裔rn美国人的数据构建了一个基因图。将该基因图rn与欧洲人基因图所做比较，显示了在祖先来自rn西非的人中活跃、但在大部分欧洲人中不活跃rn的超过2，000个重组热点。在这些热点上发生rn交叉的概率被控制在PRDM9位点上。 个rn“1 7碱基对DNA序列”主题在这些热点上被突rn显出来，它是致病性基因组重排的一个隐患。
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