Average number of amino acid and nucleotide differences per site among tra genes in different species, plus standard errors, calculated using the bootstrap method (1000 replicates).

(1) Numbers of amino acid differences per site (p-distance). (2) Number of nucleotide differences per site (p-distance). (3) Number of synonymous differences per site. (4) Number of non-synonymous differences per site. (5) Transition/transversion ratio.

(1) 每位点氨基酸差异数（p-distance）。(2) 每位点核苷酸差异数（p-distance）。(3) 每位点同义替换差异数。(4) 每位点非同义替换差异数。(5) 转换/颠换比值（Transition/transversion ratio）。