Evolution of mammalian X chromosome-linked imprinting.
We analyse the evolution of X chromosome-linked imprinting by modifying our previous model of imprinting of autosomal genes that influence the trade-off between maternal fecundity and offspring viability through alterations in maternal investment (Mills and Moore, 2004). Unlike previous genetic models, we analyse X-linked imprinting in the context of populations at equilibrium for either autosomal or X-linked biallelically expressed alleles at loci that influence the fecundity/viability trade-off. We show that selection under parental conflict over maternal investment in offspring can parsimoniously explain the occurrence of sex-specific gene expression patterns, without a requirement to postulate direct selection for sexual dimorphism mediated through imprinting. We note that sex chromosome imprinting causes a small distortion of the post-weaning sex ratio, providing a possible selection pressure against the evolution of X-linked imprints. We discuss our conclusions in the context of recent reports of imprinting of mouse X-linked Xlr genes.
Mills
W
W
Department of Biochemistry, Biosciences Institute, University College Cork, Cork, Ireland. w_e_mills@yahoo.co.uk
Moore
T
T
D000818:Animals; D019143:Evolution, Molecular; D005260:Female; D020868:Gene Silencing; D018392:Genomic Imprinting; D008297:Male; D008322:Mammals; D008425:Maternal Behavior; D012727:Sex Characteristics; D014960:X Chromosome