Lutz S, Weisser H J, Heizmann J, Pollak S
Institut für Rechtsmedizin, Klinikum der Universität Freiburg, Germany.
Int J Legal Med. 2000;113(3):155-61. doi: 10.1007/s004140050288.
The second hypervariable segment of the human mtDNA control region contains a homopolymeric tract of cytidines between nucleotides (nt) 303 and 315, interrupted by a thymidine at position 310, according to the Cambridge reference sequence. By direct sequencing, some individuals show blurred sequence chromatograms in this region which are not caused by a sequencing artefact but by high levels of length heteroplasmy. With respect to this length heteroplasmy ten maternally related individuals and two unrelated probands were examined. The relative proportions of length variants in the homopolymeric tract in selected individuals were determined by cloning and sequencing of multiple independent clones. All ten family members examined were heteroplasmic while the proportions of each genotype varied widely in different individuals. The size of a possible mitochondrial bottleneck during embryonic development of the offspring is discussed with respect to the changes in mitochondrial haplotypes within mother-offspring pairs. Our data are consistent with both slow and rapid segregation of mtDNAs between the generations, which would implicate a tight as well as a wide bottleneck. Therefore, a common bottleneck size in all individuals from this lineage seems to be very unlikely.
根据剑桥参考序列，人类线粒体DNA（mtDNA）控制区的第二个高变区在核苷酸（nt）303和315之间包含一段胞嘧啶同聚物序列，在位置310处被一个胸腺嘧啶打断。通过直接测序，一些个体在该区域显示出模糊的序列色谱图，这并非由测序假象引起，而是由高水平的长度异质性导致。针对这种长度异质性，对10名母系相关个体和2名无关先证者进行了检查。通过对多个独立克隆进行克隆和测序，确定了选定个体中同聚物序列中长度变异体的相对比例。所有10名受检家庭成员均为异质体，而每种基因型的比例在不同个体中差异很大。结合母-子对中线粒体单倍型的变化，讨论了后代胚胎发育过程中可能存在的线粒体瓶颈大小。我们的数据与mtDNA在代际间的缓慢和快速分离均相符，这意味着存在一个狭窄以及一个宽泛的瓶颈。因此，该谱系所有个体中存在共同瓶颈大小的可能性似乎非常小。
