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MBE Advance Access published online on August 5, 2004
Molecular Biology and Evolution, doi:10.1093/molbev/msh218
Molecular Biology and Evolution © Society for Molecular Biology and Evolution 2004; all rights reserved
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Accepted July 19, 2004

Original Article

Microsatellite Variation and Evolutionary History of PCDHX/Y Gene Pair within the Xq21.3/Yp11.2 Hominid-specific Homology Block

Alexandra M. Lopes 1*, Francesc Calafell 2, António Amorim 1

1 IPATIMUP, Instituto de Patologia e Imunologia Molecular da Universidade do Porto, Portugal; Faculdade de Ciências, Universidade do Porto, Portugal
2 Unitat de Biologia Evolutiva, Facultat de Ciències de la Salut i de la Vida, Universitat Pompeu Fabra, Barcelona

* To whom correspondence should be addressed. E-mail: alopes{at}ipatimup.pt.


  Abstract

To better understand the evolutionary dynamics of repetitive sequences in human sex chromosomes we have analyzed seven new X/Y homologous microsatellites located within PCDHX/Y, one of the two recently described gene pairs in the Xq21.3/Yp11.2 hominid specific homology block, in samples from Portugal and Mozambique. Sharp differences were observed on X/Y allele distributions, concerning both the presence of private alleles and a different modal repeat length for X and Y-linked markers and this difference was statistically significant (Kolmogorov-Smirnov test, P<0.001 in all X-Y pairs).

Higher diversity was found in X-linked microsatellites than in their Y chromosome counterparts; when comparing populations, Mozambicans showed more allele diversity for the X chromosome, but the contrary was true for the Y chromosome microsatellites.

Evolutionary patterns, relying on intragenic PCDHX/Y SNPs, also revealed distinct scenarios for X and Y chromosomes. Greater microsatellite diversity was displayed by African X chromosomes within the most common haplotypes shared by both populations, whilst higher microsatellite diversity was found in Portugal for the ancestral Y chromosome haplotype. The most frequent PCDHY haplotype in Portuguese was the derived one and it was not found in Mozambicans. TMRCA estimated by the {rho} parameter resulted in 13,700 years (7,500 - 20,000), which is consistent with a recent, post-Out-of-Africa origin for this haplotype.

In conclusion, the newly described microsatellite loci generally displayed greater X-linked to Y-linked diversity and this pattern was also detected with slower evolving markers, with a remarkable differentiation between populations observed for Y chromosome haplotypes and thus greater divergence among Y chromosomes in human populations.

Keywords: Microsatellite variation; sex chromosomes; ProtocadherinX/Y; Homo sapiens; evolution.
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