Tracking the Rapid Evolution of Sex Chromosome Palindromes and Their Genes

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ABSTRACT In many species, genes and genomic regions involved in male fertility evolve rapidly. Mammalian sex chromosomes are enriched for rapidly evolving large palindromic sequences harboring testis-specific genes. However, the mechanism driving rapid evolution of X- and Y- palindromes and their associated genes is poorly understood. I propose that intra-palindrome gene conversion – the “copying” of sequence from one palindrome arm to the other via recombination – is the primary mechanism driving X- and Y- palindrome evolution. The premise of this proposal is based upon observations from my recently published findings in mouse and previous studies in primates that X- and Y-palindromes, respectively, undergo on-going intra-palindrome gene conversion. To address the rapid evolution of X- and Y-palindromic sequences, I will first identify whether selective pressures (i.e. positive or purifying selection) influence the sequence evolution of X- and Y- palindromes in mice. This will be the first systematic analysis of both X- and Y-palindrome sequence evolution within a single species to understand the selective pressures governing their evolution. I will also develop a novel assay to address, for the first time, the in vivo frequencies of X- and Y- intra-palindrome gene conversion. Understanding the evolution of X- and Y- palindromes and in vivo frequencies of intra-palindrome gene conversion will provide valuable insights into the rapid evolution of genomic regions important for male fertility.