Monday, April 28, 2008

Neolithic Origin for Y-Chromosomal Variation in North Africa

The American Journal of Human Genetics

A Predominantly Neolithic Origin for Y-Chromosomal DNA Variation in North Africa.
Barbara Arredi, Estella S. Poloni, Silvia Paracchini, Tatiana Zerjal, Dahmani M. Fathallah, Mohamed Makrelouf, Vincenzo L. Pascali, Andrea Novelletto, and Chris Tyler-Smith.

We have typed 275 men from five populations in Algeria, Tunisia, and Egypt with a set of 119 binary markers and 15 microsatellites from the Y chromosome, and we have analyzed the results together with published data from Moroccan populations. North African Y-chromosomal diversity is geographically structured and fits the pattern expected under an isolation-by-distance model. Autocorrelation analyses reveal an east-west cline of genetic variation that extends into the Middle East and is compatible with a hypothesis of demic expansion. This expansion must have involved relatively small numbers of Y chromosomes to account for the reduction in gene diversity towards the West that accompanied the frequency increase of Y haplogroup E3b2, but gene flow must have been maintained to explain the observed pattern of isolation-by-distance. Since the estimates of the times to the most recent common ancestor (TMRCAs) of the most common haplogroups are quite recent, we suggest that the North African pattern of Y-chromosomal variation is largely of Neolithic origin. Thus, we propose that the Neolithic transition in this part of the world was accompanied by demic diffusion of Afro-Asiatic–speaking pastoralists from the Middle East.

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