Molecular Biology and Evolution 18:1593-1596 (2001)
© 2001 Society for Molecular Biology and Evolution
Different Patterns of Expansion/Contraction During the Evolution of an mtDNA Simple Repeat
Departments of Radiation Oncology and Human Biological Chemistry and Genetics, University of Texas Medical Branch, Galveston, Texas
MitoKor, San Diego, California
Centre for Eye Research Australia, University of Melbourne, Australia; Royal Victorian Eye and Ear Hospital, Melbourne, Australia; and the Menzies Centre for Population Health Research, University of Tasmania, Hobart, Tasmania, Australia
The human mtDNA noncoding control region contains simple homopolymeric repeat sequences that undergo expansion and contraction (Torroni et al. 1994
; Bendall and Sykes 1995
; Marchington et al. 1997
; Howell and Bogolin Smejkal 2000
). In most instances, the expansion/contraction process is sufficiently rapid that individuals are heteroplasmic and carry multiple repeat length variants. Torroni et al. (1994)
were the first group to report an expansion of the C6 repeat at nucleotides 568–573 (all mtDNA sequences presented here are those of the rCRS L-strand; Andrews et al. 1999
). They reported that mtDNAs of European haplogroup I were expanded in this repeat and carried an additional 2–6 residues. We report here that this repeat can undergo both "small" and "large" expansions (defined below) but that all such expansions appear to be unstable and prone to further expansion/contraction. Furthermore, large expansions have occurred at least twice during human evolution.
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