Pseudoautosomal region 1 length polymorphism in the human population.

Martin A Mensah,Koen Devriendt,Mala Isrie,Hilde Van Esch,Matthias Declercq,Nancy Vanderheyden,Joris R Vermeesch,Radka Stoeva,Ronny Decorte,Maarten H D Larmuseau,Erika L Souche,Matthew S Hestand,Thierry Voet,Jeroen Van Houdt,Peter N Robinson,Bret A Payseur

doi:10.1371/journal.pgen.1004578

Abstract

The human sex chromosomes differ in sequence, except for the pseudoautosomal regions (PAR) at the terminus of the short and the long arms, denoted as PAR1 and PAR2. The boundary between PAR1 and the unique X and Y sequences was established during the divergence of the great apes. During a copy number variation screen, we noted a paternally inherited chromosome X duplication in 15 independent families. Subsequent genomic analysis demonstrated that an insertional translocation of X chromosomal sequence into theMa Y chromosome generates an extended PAR. The insertion is generated by non-allelic homologous recombination between a 548 bp LTR6B repeat within the Y chromosome PAR1 and a second LTR6B repeat located 105 kb from the PAR boundary on the X chromosome. The identification of the reciprocal deletion on the X chromosome in one family and the occurrence of the variant in different chromosome Y haplogroups demonstrate this is a recurrent genomic rearrangement in the human population. This finding represents a novel mechanism shaping sex chromosomal evolution.

Highlights

The human sex chromosomes originate from an ancestral homologous chromosome pair
The human sex chromosomes differ in sequence, except for homologous sequences at both ends, termed the pseudoautosomal regions (PAR1 and PAR2)
The observation of gradual shortening of the Y chromosome over evolutionary time has led to speculations that the Y chromosome is ‘‘doomed to extinction.’’ the Y chromosome has been shaped over evolution by the loss of genes, and by addition of genes as a result of interchromosomal exchanges

Summary

Introduction

The human sex chromosomes originate from an ancestral homologous chromosome pair. During mammalian evolution, these chromosomes lost homology due to progressive degradation of the Y chromosome. The decay of the Y chromosome started with the introduction of sex determination factors, which initiated subsequent cycles of suppressed recombination [1]. Two main mechanisms are usually invoked to explain the reduction of XY homology. A stepwise reduction of recombination has been observed in the mammalian Y chromosome. It has been speculated that chromosomal rearrangements, such as inversions, might explain the stepwise decrease in sequence similarity between genes ordered on the human X chromosome and their homologs (called ‘‘gametologs’’) on the Y chromosome [3]. The forces driving recombination suppression remain to be established

Methods

Results

Discussion

Conclusion