Significant levels of sequence divergence and gene rearrangements have occurred between the mitochondrial genomes of the wild mulberry silkmoth, Bombyx mandarina, and its close relative, the domesticated silkmoth, Bombyx mori.

The metazoan mitochondrial (mt) genome is typically a circular, double-stranded DNA molecule between 14 and 18 kb in size. This molecule encodes 37 genes: 13 protein genes, 2 ribosomal RNA genes, and 22 tRNA genes (Wolstenholme 1992). The order of these genes varies among metazoans (Boore 1999). The mt genomes of 14 insects have been completely sequenced. These include (1) seven flies (Diptera), Drosophila yakuba (Clary and Wolstenholme 1985— X03240), D. melanogaster (Lewis, Farr, and Kaguni 1995—U37541), D. mauritiana, D. sechellia, D. simulans (Ballard 2000—AF200830 and AF200831 for D. mauritiana, AF200832 for D. sechellia, and AF200834, AF200841, and AF200852 for D. simulans), Ceratitis capitata (Spanos et al. 2000—AJ242872), and Cochliomyia himinivorax (Lessinger et al. 2000—AF260826); (2) two mosquitoes (Diptera), Anopheles quadrimaculatus (Mitchell, Cockburn, and Seawright 1993— L04272) and A. gambiae (Beard, Hamm, and Collins 1993—L20934); (3) the domesticated silkmoth (Lepidoptera), Bombyx mori, the Backokjam strain (Lee et al., unpublished data, but available in GenBank, accession number AF149768); (4) the honeybee (Hymenoptera), Apis mellifera (Crozier and Crozier 1993—L06178); (5) the locust (Orthoptera), Locusta migratoria (Flook, Rowell, and Gellisson 1995—X80245); (6) the kissing bug (Hemiptera), Triatoma dimidiata (Dotson and Beard 2001—AF301594); and (7) the Wallaby louse (Phthiraptera), Heterodoxus macropus (Shao, Campbell, and Barker 2001—AF270939). In all sampled insects other than the Wallaby louse, all mt gene rearrangements involve only tRNA genes. Bombyx mandarina is a probable wild ancestor of the domesticated silkmoth, B. mori. Bombyx mandarina includes significant variation within species, e.g., a difference in chromosome number: whereas 27 chromosomes are seen in the haploid genome of this organism