Self-imposed silence: parental antagonism and the evolution of X-chromosome inactivation.
A model is proposed for the evolution of X-chromosome inactivation (XCI) in which natural selection initially favors the silencing of paternally derived alleles of X-linked demand inhibitors. The compensatory upregulation of maternally derived alleles establishes a requirement for monoallelic expression in females. For this reason, XCI is self-reinforcing once established. However, inactivation of a particular X chromosome is not. Random XCI (rXCI) is favored over paternal XCI because rXCI reduces the costs of functional hemizygosity in females. Once present, rXCI favors the evolution of locus-by-locus imprinting of X-linked loci, which creates an evolutionary dynamic in which different chromosomes compete to remain active.
Haig
David
D
Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138, USA. dhaig@oeb.harvard.edu
D000818:Animals; D005075:Biological Evolution; D004303:Dosage Compensation, Genetic; D005260:Female; D050172:Genes, X-Linked; D008297:Male; D008954:Models, Biological; D049951:X Chromosome Inactivation