Fig. 2.
Sequence evolution of T. muenninki neo-sex chromosomes. a Nucleotide sequence evolution in the coding sites of 17 combined genes. b Nucleotide sequence evolution in the noncoding sites of 18 combined genes. Equality of the evolutionary rate between the neo-X and neo-Y was rejected based on a chi-squared test, and an accelerated rate of evolution in the neo-Y was demonstrated in both coding and noncoding sites. subs: substitutions. c Maximum likelihood tree of the coding sequences of 17 combined genes. Numbers above and under branches refer to dN/dS ratios and maximum-likelihood bootstrap percentage (1000 replications), respectively. The free-ratio model is used, which assumes a different dN/dS ratio for each branch in the tree. dS: synonymous substitution rate; dN: non-synonymous substitution rate; spiny rat: T. muenninki; mouse: M. musculus; rat: R. norvegicus