The genus Paedocypris is a newly described taxon of minifish species that are characterized by
extensive chromosome evolution and one of the smallest known vertebrate nuclear genomes. Paedocypris
features a tiny adult size, a short generation time, low fecundity and fragmented tropical habitats, which are
factors that favor rapid speciation. Most recently, we have revealed that P. progenetica (Pp), the type species
of the genus Paedocypris, has an unusual mtDNA bearing - within its D-loop - a tandem array of a 34-bp
repeat sequence called the minifish repeat, which shows compromised replication efficiency in vitro. Here we
report that Pp exhibits high genetic variation in mtDNA size. The efficiency of D-loop amplification was found to
depend upon primers. Interestingly, Pp individuals of one and the same population differed drastically in
mtDNA size resulting from varying copy numbers of the minifish repeat. We conclude that minifish has a high
mutation rate and perhaps represents a rapidly evolving taxon of vertebrates.
Keywords: D-loop, genetic variation, heteroplasmy, minifish repeat, mtDNA.
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