An improved method for determining codon variability in a gene and its application to the rate of fixation of mutations in evolution

摘要: If one has the amino acid sequences of a set homologous proteins as well their phylogenetic relationships, can easily determine minimum number mutations (nucleotide replacements) which must have been fixed in each codon since common ancestor. It is found that for 29 species cytochrome c data fit assumption there group approximately 32 invariant codons and remainder compose two Poisson-distributed groups size 65 16 codons, latter smaller fixing at about 3.2 times rate larger. further increases range narrowed. Extrapolation suggests less than 10% given mammalian gene are capable accepting mutation. This consistent with view any point time only very restricted positions fix but also change so examination wide reveals altered positions. We define this concomitantly variable codons. Given restriction, fixation rates fibrinopeptide A not different, result should be case if most these fact selectively neutral Kimura suggests.