Patterns of Inter-Chromosomal Gene Conversion on the Male-Specific Region of the Human Y Chromosome

Abstract

The male-specific region of the human Y chromosome (MSY) is characterized by the lack of meiotic recombination and it has long been considered an evolutionary independent region of the human genome. In recent years, however, the idea that human MSY did not have an independent evolutionary history begun to emerge with the discovery that inter-chromosomal gene conversion (ICGC) can modulate the genetic diversity of some portions of this genomic region. Despite the study of the dynamics of this molecular mechanism in humans is still in its infancy, some peculiar features and consequences of it can be summarized. The main effect of ICGC is to increase the allelic diversity of MSY by generating a significant excess of clustered single nucleotide polymorphisms (SNPs) (defined as groups of two or more SNPs occurring in close proximity and on the same branch of the Y phylogeny). On the human MSY, 13 inter-chromosomal gene conversion hotspots (GCHs) have been identified so far, involving donor sequences mainly from the X-chromosome and, to a lesser extent, from autosomes. Most of the GCHs are evolutionary conserved and overlap with regions involved in aberrant X–Y crossing-over. This review mainly focuses on the dynamics and the current knowledge concerning the recombinational landscape of the human MSY in the form of ICGC, on how this molecular mechanism may influence the evolution of the MSY, and on how it could affect the information enclosed within a genomic region which, until recently, appeared to be an evolutionary independent unit.

Convergent evolution of linked mating-type loci in basidiomycete fungi

“…In C. neoformans, gene conversion occurred in a GC-rich intergenic region within the MAT locus and was proposed as a mechanism for maintaining functionality of those genes within the MAT locus that are essential [39]. Gene conversion has also been observed in regions with suppressed recombination in the mating-type chromosomes of N. tetrasperma, in the mating type locus of the green algae Chlamydomonas reinhardtii, and in sex chromosomes of animals [95][96][97][98][99][100][101].…”

Dynamic evolution of great ape Y chromosomes

“…The X-degenerate regions are composed of segments with different levels of homology to the X chromosome, which are called strata, corresponding to stepwise losses of X-Y recombination. Because of lack of recombination (except for occasional X-Y gene conversion ( 10 , 11 ), X-degenerate regions are expected to accumulate gene-disrupting mutations; however, this has not been examined in detail. The ampliconic regions consist of repetitive sequences that have >50% identity to each other and contain palindromes—inverted repeats (separated by a spacer) up to several megabases long the arms of which are >99.9% identical ( 6 ).…”

Consequences of recombination for the evolution of the mating type locus in Chlamydomonas reinhardtii

“…Additionally, unlike crossovers, gene conversions can occur between inversions (Korunes & Noor, ), as previously observed in the R domain of MT (De Hoff et al ., ). Similar patterns of periodic interchromosomal gene conversion for putatively adaptive purposes have been observed in the sex chromosomes of European tree frogs (Stöck et al ., ), avian sex chromosomes (Wright et al ., ), fungal mating‐type loci (Menkis et al ., ; Sun et al ., ), and certain mammalian sex‐linked orthologues (Pecon Slattery et al ., ; Rosser et al ., ; Peneder et al ., ; Trombetta et al ., ). However, the effect of gene conversion on selection efficacy in these regions has not yet been investigated.…”