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Open Access Research article

X-chromosome SNP analyses in 11 human Mediterranean populations show a high overall genetic homogeneity except in North-west Africans (Moroccans)

Carmen Tomas1*, Juan J Sanchez12, Anna Barbaro3, Conxita Brandt-Casadevall4, Alexis Hernandez2, Mohamed Ben Dhiab5, Misericordia Ramon6 and Niels Morling1

Author Affiliations

1 Section of Forensic Genetics, Department of Forensic Medicine, Faculty of Health Sciences, University of Copenhagen, Copenhagen, Denmark

2 Instituto Nacional de Toxicología y Ciencias Forenses, Delegación de Canarias, Tenerife, Spain

3 Sezione di Genetica Forense, SIMEF (Studio Indagini Mediche E Forensi), Reggio Calabria, Italy

4 Institut Universitaire de Médecine Légale, Lausanne, Switzerland

5 Service de Médecine Légale, Hôpital Farhat Hached, Sousse, Tunisia

6 Institut Universitari d'Investigacions en Ciències de la Salut i Laboratori de Genètica, Departament de Biologia, Universitat de les Illes Balears, Palma de Mallorca, Spain

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BMC Evolutionary Biology 2008, 8:75  doi:10.1186/1471-2148-8-75

Published: 29 February 2008

Abstract

Background

Due to its history, with a high number of migration events, the Mediterranean basin represents a challenging area for population genetic studies. A large number of genetic studies have been carried out in the Mediterranean area using different markers but no consensus has been reached on the genetic landscape of the Mediterranean populations. In order to further investigate the genetics of the human Mediterranean populations, we typed 894 individuals from 11 Mediterranean populations with 25 single-nucleotide polymorphisms (SNPs) located on the X-chromosome.

Results

A high overall homogeneity was found among the Mediterranean populations except for the population from Morocco, which seemed to differ genetically from the rest of the populations in the Mediterranean area. A very low genetic distance was found between populations in the Middle East and most of the western part of the Mediterranean Sea.

A higher migration rate in females versus males was observed by comparing data from X-chromosome, mt-DNA and Y-chromosome SNPs both in the Mediterranean and a wider geographic area.

Multilocus association was observed among the 25 SNPs on the X-chromosome in the populations from Ibiza and Cosenza.

Conclusion

Our results support both the hypothesis of (1) a reduced impact of the Neolithic Wave and more recent migration movements in NW-Africa, and (2) the importance of the Strait of Gibraltar as a geographic barrier. In contrast, the high genetic homogeneity observed in the Mediterranean area could be interpreted as the result of the Neolithic wave caused by a large demic diffusion and/or more recent migration events. A differentiated contribution of males and females to the genetic landscape of the Mediterranean area was observed with a higher migration rate in females than in males. A certain level of background linkage disequilibrium in populations in Ibiza and Cosenza could be attributed to their demographic background.