Molecular clock hypothesis testing based on mitochondrial cytochrome b gene sequence of subfamily bovinae

To provide some objective data for accepting or refusing molecular clock hypothesis,non-parameter test method was employed based on mitochondrial cytochrome b gene sequence of six species of subfamily bovinae.The complete cytochrome b gene was 1 140 bp in length for all six bovine species and there was a little difference in base composition between species.Transition was the dominant base substitution model and the ratio of transition to transversion was 5.4.The testing results of relative evolution rate based on nucleotide sequences and amino acid sequences showed that molecular clock hypothesis was accepted absolutely within bovine species.The evolution of only a few sequences refused molecular clock hypothesis and evolution of most sequences accepted it among the species.It was easier to refuse molecular clock hypothesis based on the testing result from nucleotide sequence than the result from amino acid sequence.There was no obvious correlation between accepting or refusing molecular clock hypothesis and genetic distance between tested species.Molecular clock existed in some species.There was no nucleotide sequence or amino acid sequence varying in an absolutely stable rate in long evolution,and molecular clock was not unicersal.