Table of Contents
International Journal of Evolutionary Biology
Volume 2012 (2012), Article ID 207958, 14 pages
http://dx.doi.org/10.1155/2012/207958
Review Article

Why Chromosome Palindromes?

Department of Biology, University of Texas at Arlington, Box 19498, Arlington, TX 76019, USA

Received 31 March 2012; Accepted 9 May 2012

Academic Editor: Hideki Innan

Copyright © 2012 Esther Betrán et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract

We look at sex-limited chromosome (Y or W) evolution with particular emphasis on the importance of palindromes. Y chromosome palindromes consist of inverted duplicates that allow for local recombination in an otherwise nonrecombining chromosome. Since palindromes enable intrachromosomal gene conversion that can help eliminate deleterious mutations, they are often highlighted as mechanisms to protect against Y degeneration. However, the adaptive significance of recombination resides in its ability to decouple the evolutionary fates of linked mutations, leading to both a decrease in degeneration rate and an increase in adaptation rate. Our paper emphasizes the latter, that palindromes may exist to accelerate adaptation by increasing the potential targets and fixation rates of incoming beneficial mutations. This hypothesis helps reconcile two enigmatic features of the “palindromes as protectors” view: (1) genes that are not located in palindromes have been retained under purifying selection for tens of millions of years, and (2) under models that only consider deleterious mutations, gene conversion benefits duplicate gene maintenance but not initial fixation. We conclude by looking at ways to test the hypothesis that palindromes enhance the rate of adaptive evolution of Y-linked genes and whether this effect can be extended to palindromes on other chromosomes.