title: Gene conversion violates the stepwise mutation model for microsatellites in y-chromosomal palindromic repeats.
abstract: The male-specific region of the human Y chromosome (MSY) contains eight large inverted repeats (palindromes), in which high-sequence similarity between repeat arms is maintained by gene conversion. These palindromes also harbor microsatellites, considered to evolve via a stepwise mutation model (SMM). Here, we ask whether gene conversion between palindrome microsatellites contributes to their mutational dynamics. First, we study the duplicated tetranucleotide microsatellite DYS385a,b lying in palindrome P4. We show, by comparing observed data with simulated data under a SMM within haplogroups, that observed heteroallelic combinations in which the modal repeat number difference between copies was large, can give rise to homoallelic combinations with zero-repeats difference, equivalent to many single-step mutations. These are unlikely to be generated under a strict SMM, suggesting the action of gene conversion. Second, we show that the intercopy repeat number difference for a large set of duplicated microsatellites in all palindromes in the MSY reference sequence is significantly reduced compared with that for nonpalindrome-duplicated microsatellites, suggesting that the former are characterized by unusual evolutionary dynamics. These observations indicate that gene conversion violates the SMM for microsatellites in palindromes, homogenizing copies within individual Y chromosomes, but increasing overall haplotype diversity among chromosomes within related groups.
authors.affiliation: UMR5288 CNRS/UPS-AMIS-Université Paul Sabatier, Toulouse, France; Department of Genetics, University of Leicester, Leicester, UK.
authors.forename: Patricia
authors.initials: P
authors.lastname: Balaresque
authors.forename: Turi E
authors.initials: TE
authors.lastname: King
authors.forename: Emma J
authors.initials: EJ
authors.lastname: Parkin
authors.forename: Evelyne
authors.initials: E
authors.lastname: Heyer
authors.forename: Denise
authors.initials: D
authors.lastname: Carvalho-Silva
authors.forename: Thirsa
authors.initials: T
authors.lastname: Kraaijenbrink
authors.forename: Peter
authors.initials: P
authors.lastname: de Knijff
authors.forename: Chris
authors.initials: C
authors.lastname: Tyler-Smith
authors.forename: Mark A
authors.initials: MA
authors.lastname: Jobling
mesh_terms: D041322:Chromosomes, Human, Y / Q000235:genetics; D005785:Gene Conversion; D006801:Humans; D055029:Inverted Repeat Sequences / Q000235:genetics*; D018895:Microsatellite Repeats / Q000235:genetics*; D008957:Models, Genetic; D009154:Mutation
keywords: DYS385; Y chromosome; gene conversion; microsatellite; palindrome; stepwise mutation model