Rates of nucleotide substitution in Drosophila mitochondrial DNA and nuclear DNA are similar

While the majority of DNA in eukaryotes is in the nucleus, a small but functionally significant amount is found in organelles such as chloroplasts and mitochondria. A recent, rather remarkable, finding has been that in vertebrates the DNA in the mitochondria (mtDNA) is evolving 5-10 times faster than the DNA in the nucleus. No similar studies have been done with invertebrates. Using the technique of DNA X DNA hybridization, we have measured the degree of nucleotide substitution between Drosophila melanogaster and Drosophila yakuba for both single-copy nuclear DNA (scnDNA) and mtDNA. The change in melting temperature is the same in both types of DNA hybrids. Thus we conclude that mtDNA and scnDNA are evolving at similar rates in these Drosophila. Considerable DNA sequence data are available for the mtDNAs studied, allowing us to estimate that a 1 degree C change in melting temperature corresponds to a 1.5-2% base-pair mismatch.