Abstract
In the last two decades, mitochondrial DNA (mtDNA) and the non-recombining portion of the Y chromosome (NRY) have been extensively used in order to measure the maternally and paternally inherited genetic structure of human populations, and to infer sex-specific demography and history. Most studies converge towards the notion that among populations, women are genetically less structured than men. This has been mainly explained by a higher migration rate of women, due to patrilocality, a tendency for men to stay in their birthplace while women move to their husband's house. Yet, since population differentiation depends upon the product of the effective number of individuals within each deme and the migration rate among demes, differences in male and female effective numbers and sex-biased dispersal have confounding effects on the comparison of genetic structure as measured by uniparentally inherited markers. In this study, we develop a new multi-locus approach to analyze jointly autosomal and X-linked markers in order to aid the understanding of sex-specific contributions to population differentiation. We show that in patrilineal herder groups of Central Asia, in contrast to bilineal agriculturalists, the effective number of women is higher than that of men. We interpret this result, which could not be obtained by the analysis of mtDNA and NRY alone, as the consequence of the social organization of patrilineal populations, in which genetically related men (but not women) tend to cluster together. This study suggests that differences in sex-specific migration rates may not be the only cause of contrasting male and female differentiation in humans, and that differences in effective numbers do matter.
Highlights
Understanding the extent to which sex-specific processes shape human genetic diversity has long been a matter of great interest for human population geneticists [1,2]
In order to recognize the impact of social organization on these differences, we investigate sex-specific genetic structure in human populations of Central Asia (Figure 1), where various ethnic groups, characterized by different languages, lifestyles and social organizations, co-exist
This new multilocus approach is, to our knowledge, the first attempt to combine the information contained in mitochondrial DNA (mtDNA), nonrecombining portion of the Y chromosome (NRY), X-linked and autosomal markers, which allowed us to test for the robustness of a sex-specific genetic structure at a local scale
Summary
Understanding the extent to which sex-specific processes shape human genetic diversity has long been a matter of great interest for human population geneticists [1,2]. A large number of studies have found that the level of differentiation was greater for the Y chromosome than for mtDNA, both at a global [3] and a local scale [4,5,6,7,8,9,10,11], for a review see [12] This result has mainly been explained by patrilocality, a widespread tendency for men to stay in their birthplace while women move to their husband’s house [13] (see Table 1 for more detailed interpretations). The apparent paradox between local and global trends can be resolved though, since the geographical clustering of populations with potentially
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