Figure 1.

Synteny and age of sex chromosomes across amniote lineages. The data on synteny are presented in the electronic supplementary material, table 1. The age of divergence between clades and the minimal age of sex chromosomes (estimated as the split between the phylogenetically most distant members of a clade with evidence for homology of sex chromosomes) are taken from Kumar et al. [25], available at http://timetree.org. The numbers next to the clade names represent the estimated number of species putatively sharing the given sex chromosomes. The phylogenetic tree follows Shen et al. [26] for the topology of major lineages and Pyron et al. [27] for squamates. Corytophanids might form an inner group of Pleurodonta, but this question is not resolved yet [28]. mg, ‘missing genes’ in chicken. (Online version in colour.)