Between-Group Variation is similar for Y-chromosomes and mtDNA

A new study has discovered that the between-group variation variation in human Y-chromosomes and mtDNA is similar (0.334 vs. 0.382). This has three important implications:

• It was previously thought that since women tend to move to their husbands' homes, female genes travelled wider than men's, "homogenizing" the mitochondrial gene pool of mankind. This new research disproves this idea, as human populations are differentiated about the same in their Y-chromosomes and mtDNA.
  
• The higher female effective population size throughout human prehistory (a widely accepted idea) together with these new results lead to the conclusion that "our observation of roughly equal between-group components of variation for the Y chromosome and mtDNA implies a lower rate of migration for females than for males among the widely spaced populations we surveyed." In other words, men's genes travelled more than women's.
  
• Previous estimates of Y-chromosome diverstiy used single-nucleotide polymorphisms (SNPs) which were known to vary between populations. As a result, Y-chromosome population differentiation tended to be overemphasized in the past. On the other hand for mtDNA studies used hypervariable portions of the control region where mutation rates are higher than in coding regions (that actually do useful stuff). Therefore, mtDNA population differentiation tended to be underestimated in the past.

It will certainly be interesting to watch for new studies on other genetic loci using the strategy of Wilder et al. to assess between-population differentiation. The supposed low level of genetic differentiation between global populations is after all one of the main arguments of the race doesn't exist crowd.

Nature Genetics (Published online: 19 September 2004; | doi:10.1038/ng1428)

Global patterns of human mitochondrial DNA and Y-chromosome structure are not influenced by higher migration rates of females versus males

Jason A Wilder et al.

Global-scale patterns of human population structure may be influenced by the rate of migration among populations that is nearly eight times higher for females than for males. This difference is attributed mainly to the widespread practice of patrilocality, in which women move into their mates' residences after marriage1. Here we directly test this hypothesis by comparing global patterns of DNA sequence variation on the Y chromosome and mitochondrial DNA (mtDNA) in the same panel of 389 individuals from ten populations (four from Africa and two each from Europe, Asia and Oceania). We introduce a new strategy to assay Y-chromosome variation that identifies a high density of single-nucleotide polymorphisms, allows complete sequencing of all individuals rather than relying on predetermined markers and provides direct sequence comparisons with mtDNA. We found the overall proportion of between-group variation (Phi ST) to be 0.334 for the Y chromosome and 0.382 for mtDNA. Genetic differentiation between populations was similar for the Y chromosome and mtDNA at all geographic scales that we tested. Although patrilocality may be important at the local scale2, 3, patterns of genetic structure on the continental and global scales are not shaped by the higher rate of migration among females than among males.

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