Differential rates of evolution for the ZFY-related zinc finger genes, Zfy, Zfx, and Zfa in the mouse genus Mus

A comparative study of the last exon of the zinc finger genes Zfx, Zfy, and Zfa from species of mice in the genus Mus was conducted to assess the extent of gene-specific and chromosome-specific effects on the evolutionary patterns among related X-, Y-, and autosomal-linked genes. Phylogenetic analyses of 29 sequences from Zfx, Zfa, and Zfy from 10 taxa were performed to infer relatedness among the zinc finger loci, and codon-based maximum likelihood analyses were conducted to assess evolutionary pattern among genes. Five models of nucleotide sequence evolution were applied and compared using a likelihood ratio test. Estimates of nonsynonymous to synonymous changes (d_N/d_S) for these genes suggest that amino acid substitutions are occurring at a more rapid rate across the autosomal- and Y-specific lineages compared to the X-specific lineage, with the Y-specific lineage showing the highest rate under certain models. The data suggest the action of gene-specific effects on evolutionary pattern. In particular, Zfa and Zfy genes, both with presumed restricted expression, appear less functionally constrained relative to ubiquitously expressed Zfx. Slightly elevated d_N/d_S for Zfy genes in comparison to Zfa also suggest Y-specific effects.