Data from: Evolutionary dynamics of the gametologous CTNNB1 gene on the Z and W chromosomes of snakes

Snakes exhibit genotypic sex determination with female heterogamety (ZZ males and ZW females), and the state of sex chromosome differentiation also varies among lineages. To investigate the evolutionary history of homologous genes located in the non-recombining region of differentiated sex chromosomes in snakes, partial sequences of the gametologous CTNNB1 gene were analyzed for 12 species belonging to henophid (Cylindrophiidae, Xenopeltidae, and Pythonidae) and caenophid snakes (Viperidae, Elapidae, and Colubridae). Nonsynonymous/synonymous substitution ratios (Ka/Ks) in coding sequences were low (Ka/Ks < 1) between CTNNB1Z and CTNNB1W, suggesting that these two genes may have similar functional properties. However, frequencies of intron sequence substitutions and insertion-deletions were higher in CTNNB1Z than CTNNB1W, suggesting that Z-linked sequences evolved faster than W-linked sequences. Molecular phylogeny based on both intron and exon sequences showed the presence of two major clades: (1) Z-linked sequences of Caenophidia, and (2) W-linked sequences of Caenophidia clustered with Z-linked sequences of Henophidia, which suggests that the sequence divergence between CTNNB1Z and CTNNB1W in Caenophidia may have occurred by the cessation of recombination after the split from Henophidia.

蛇类采用雌性异配型的基因型性别决定机制（雄性为ZZ，雌性为ZW），且不同演化支的性染色体分化程度存在差异。为探究蛇类分化型性染色体非重组区同源基因的演化历史，本研究对隶属于原蛇下目（Henophidia，包含筒蛇科、闪皮蛇科及蟒科）和新蛇下目（Caenophidia，包含蝰科、眼镜蛇科及游蛇科）的12个物种的配子同源CTNNB1基因（gametologous）的部分序列进行了分析。编码区序列中CTNNB1Z与CTNNB1W的非同义替换/同义替换比值（Ka/Ks）较低（Ka/Ks < 1），提示二者可能具有相似的功能特性。但CTNNB1Z的内含子序列替换与插入缺失变异的发生频率高于CTNNB1W，表明Z染色体连锁序列的演化速率快于W染色体连锁序列。基于内含子与外显子序列构建的分子系统发育树显示存在两个主要演化支：(1) 新蛇下目的Z染色体连锁序列；(2) 新蛇下目的W染色体连锁序列与原蛇下目的Z染色体连锁序列聚类。该结果表明，新蛇下目中CTNNB1Z与CTNNB1W的序列分化，可能是在与原蛇下目分化之后，由于重组终止而产生的。