Study On The Molecular Evolution And Phylogeny Of Cytochrome B(Cyt-b) Sequence Of Domestic Goose

Mitochondrial cytochrome b(Cyt-b) sequence were used to study the molecular evolution and phylogeny of Anser cygnoides(15 breed of Chinese goose), Anser anser(2 breed of domestic European goose) and Anser albifrons(the lesser white-fronted goose, Genbank accession number AF363031). Sequence analysis revealed that there were 29 variable sites and 4 haplotypes in 45 sequences, nucleotide diversity and haplotype diversity were 0.0068,0.45 respectively, insertion/deletion or frameshift mutation were not found in Cyt-b gene sequences(1143bp). The average percent value of G+C (49.3%) was less than that of A+T (50.7%), there was a bias of the content of G, T in the third codon; The number of transition G-A and T-C were 22, 15 respectively, which were higher than that of transition A-G and C-T, the number of tranversion C-A, T-G is 2 respectively, and other tranversion patterns didn't occur; the probability of transition (Ts) was higher than that of tranversion (Tv) , Ts/Tv = 9.5-19, there was the highest number of transition in the third codon. The gamma parameter a of the lst,nd and 3rd codon positions were 0.00572,0.01237 and 1.05239 respectively, they showed that there was adifferent substitution rate at different codon position. Frequences of synonymous codon usage were relatively biased. The average rates of synonymous(dS) and nonsynonymous substitution(dN) were 0.0787, 0.0011 respectively, there was a significant difference between dS and dN (Z = 4.713, p<0.01) , and the low ratio( CD = 0.0284 <0.3) of dN/dS ratio impled that there were selective constraints against the nonsynonymous sites in cyt-b gene, The distribution of nonsynonymous codon substitution pattern related to Grantharm distance indicated that the purified selection at 2nd codon positions was more intensive than that at 1st codon positions. The phylogenetic trees supported the view of the double origin of Chinese goose, which means that domestic Chinese goose(excluding Yili) was derived from Anser cygnoides and domestic European goose(Landoise,Rhin), and Yili was derived from Anser anser.