Analysis of nucleotide substitutions of mitochondrial DNAs in Drosophila melanogaster and its sibling species |
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Authors: | Satta Y; Ishiwa H; Chigusa SI |
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Institution: | Department of Biology, Ochanomizu University, Tokyo, Japan. |
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Abstract: | To study the rate and pattern of nucleotide substitution in mitochondrial
DNA (mtDNA), we cloned and sequenced a 975-bp segment of mtDNA from
Drosophila melanogaster, D. simulans, and D. mauritiana containing the
genes for three transfer RNAs and parts of two protein- coding genes, ND2
and COI. Statistical analysis of synonymous substitutions revealed a
predominance of transitions over transversions among the three species, a
finding differing from previous results obtained from a comparison of D.
melanogaster and D. yakuba. The number of transitions observed was nearly
the same for each species comparison, including D. yakuba, despite the
differences in divergence times. However, transversions seemed to increase
steadily with increasing divergence time. By contrast, nonsynonymous
substitutions in the ND2 gene showed a predominance of transversions over
transitions. Most transversions were between A and T and seemed to be due
to some kind of mutational bias to which the A + T-rich mtDNA of Drosophila
species may be subject. The overall rate of nucleotide substitution in
Drosophila mtDNA appears to be slightly faster (approximately 1.4 times)
than that of the Adh gene. This contrasts with the result obtained for
mammals, in which the mtDNA evolves approximately 10 times faster than
single-copy nuclear DNA. We have also shown that the start codon of the COI
gene is GTGA in D. simulans and GTAA in D. mauritiana. These codons are
different from that of D. melanogaster (ATAA).
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