Hartl D L
Washington University School of Medicine, St Louis, Missouri.
Curr Opin Genet Dev. 1992 Dec;2(6):937-42. doi: 10.1016/s0959-437x(05)80119-4.
Population data suggest that many parasitic protozoa (e.g. Trypanosoma, Leishmania, Entamoeba and Giardia) reproduce clonally, but this hypothesis has been highly controversial for Plasmodium falciparum. Although reproduction is predominantly clonal in the enteric bacteria Escherichia coli and Salmonella, the level of recombination affecting short (< 1 kb) regions of the chromosome is sufficient such that many genes are obviously mosaics of different ancestries. Transposable insertion sequences in E. coli are examples of selfish DNA whose short-term population dynamics are determined mainly by transposition and horizontal transmission among strains balanced against the regulation of transposition as a function of copy number, and negative effects on fitness. Occasional advantageous effects of transposable elements have also been documented.
种群数据表明，许多寄生原生动物（如锥虫、利什曼原虫、内阿米巴和贾第虫）进行无性繁殖，但这一假说对于恶性疟原虫一直存在很大争议。虽然肠道细菌大肠杆菌和沙门氏菌主要进行无性繁殖，但影响染色体短片段（<1 kb）区域的重组水平足以使许多基因明显成为不同谱系的嵌合体。大肠杆菌中的转座插入序列是自私DNA的例子，其短期种群动态主要由转座以及菌株间的水平传播决定，同时受到作为拷贝数函数的转座调控以及对适应性的负面影响的平衡。转座元件偶尔产生的有利影响也有文献记载。
