Sequencing And Phylogenetic Analysis Of Partial MtDNA Of Samia Cynthia Ricini And Antheraea Yamamai

The animal mitochondria is highly compact annular genome, coding 2 rRNAs (16S and 12S rRNA), 22tRNA, and 13 proteins (COI-III, Cytb, ND1-6, ND4L, ATP6, and ATP8). Because easy to separation and much copy, mitpchondrial DNA become a mark of molecule evolution research which was used extensively. Make use of mtDNA polymorphism to probe into insect group , phylogenetic relationships is the focus of systematics of insects at present. It is more to study abroad, but at home, because of the limitations of such respects as experimental technique , data analysis and funds ,etc. and there is not yet much research in this field at present.Besides silkworm, Samia cynthia ricini and Antheraea yamamai are all Lepidoptera, Saturniidae and spun silk insect of higher economic worth. Actually few to research that they carry on at present, use Samia cynthia ricini mtDNA for insect molecular systematics less, and has not seen yet with Antheraea yamamai mtDNA. For this reason, we had amplified and sequencing respectively such 4 protein-coding genes as COI , COII , ATP8 , ATP6 of the Samia cynthia ricini and Antheraea yamamai mitochondrial genome, analysizing sequence of them makeup characteristics , and combining the forty-four insects which have already announce the mitochondria genome whole sequence for the phylogenetic analyse, and also appraising the phylogenetic utility of mtDNA based on morphologic taxology. The main results are as follows: 1 The sequence analysisNucleotide and amino acid frequencies of COI , COII , ATP8 , ATP6 gene was analysized.According to invertebrate's mitochondrial DNA codon (Codon5, translate-table =5),carry on the translation of the sequence. The results show that the total length of COI gene is 1558bp and of COD gene is 684bp and of ATP8 gene is 156bp and of ATP6 gene is 672bp in Samia cynthia ricini. The total length of COI gene is 1528bp and of COII gene is 681bp and of ATP8 gene is 168bp and of ATP6 gene is 681bp in Antheraea yamamai. The nucleotide makeup of four protein-coding genes are bias of A and T ,and A +T average content is higher than G +C average content obviously. In terms of makeup of the amino acids, they favorite the third is an A codons, but use the third less is a C codons.2 The phylogenetic analysisCOI , COII , ATP8 and ATP6 gene of Scania cynthia ricini and Antheraea yamamai and forty-four insects which have already announce the mitochondria genome whole sequence were used for the phylogenetic analyse. The sequences were aligned separately and combine by ClustalX.And MEGA2.0 software was used to construct the cladogram.The results of phylogenetic analysis are as follows:The complete sequence , the first and second sites of codons and amino acid sequence of COI gene were used to construct cladogram separately . The resolution of cladogram with the first and second sites of codons COI gene is the best, and higher than with amimo acid sequence . The resolution of cladogram with complete sequence of COI gene was the lowest and even the insects of intra-Diptera couldn't cluster to be together . This show that the phylogenetic utility of DNA and amino acid sequence of a same gene is different. And also the first, second sites of codons and the first ,second and third sites of codons is different.Among the four protein-coding genes , the phylogenetic utility of ATP8 gene is the lowest .The insects of Aleyrodidae were cluster to be together in cladogram of COI, COII and ATP6 gene.But they couldn't cluster in cladogram of ATP8 gene.This show that the phylogenetic utility of different gene is different and also in same taxon level is different. This suggest that we should select gene with mutation rate which match with the divergence time of lineage as molecular marker when we research the molecular systematics of some species. At the same time , evaluate the distribution of variable sites of the gene accurately is vital to detect the phylogenetic utility of gene in a given taxon. In addition ,select several genes maybe better a choice when we evaluate species trees.The resolution of cladogram of combined four genes' sequence are higher than single ATP8 gene or ATP6 gene, show that combining sequence sets is the better choice when we use several genes at the same time to research the phylogenetic relationships of species. So that the homogeneity of diversified level maybe contribute to a comprehensive and powerful signal. At the same time ,we use the other nine protein-coding genes in mitochondria genome of forty-four insects which have already announce the mitochondria genome whole sequence for the phylogenetic analysis. The result show that: the resolution of cladogram of whole genome is lower than amino acid sequence of combined nine genes or other single gene's. This suggest that mitochondria genome is not the best choice when we couldn't ascertain the phylogeny of any species.