单细胞生物进化研究的进步

The Basic Outline of the Evolution of Single Cell Life-form

20世纪 6 0年代 ,生物大致分为 5界的谱系图 ,经历了几次翻新 ,开始提出了线粒体和叶绿体的内共生学说。由于分子生物学的发展 ,首先将各种生物的蛋白质的分子进行比较 ,构建成蛋白质的分子系统树。再转向核糖核酸 ,将核糖体的小亚单位 ,作为区别生命类型之间亲缘关系的指标。发现有些嗜极端条件的细菌 ,它们不同于原核生物也不同于真核生物 ,是第三种类型的生命形式。因此 ,在 80年代为生命建立了细菌、古细菌和真核生物三界的系统树。对许许多多单个基因的系统树的分析 ,又使人们认识到 ,古细菌与细菌和真核微生物之间以及各个物种之间 ,显然皆发生过大量的基因交换。对单细胞进化来说 ,基因除垂直传递外 ,横向的或叫侧向的基因转移也十分繁多。在一张完全的系统图中 ,要同时表现几千个不同的基因家族的超联结的种系型式才符合实际。因而 ,最新版本的系统树是分枝交缠、无主干的。

In 1960s,kimgdoms of organisms were charted generally in a five branching form.Later,the endosymbiont hypothesis for the mitochondria and the chloroplast was proposed.The life-form is divided into two forms,the prokaryotes (bacteria) and the eukaryotes.The study of the molecular biology made the progress faster.In 1980s,Woese,CR.asserted that two-domain view of life was no longer true,a three-domain construct,the Bacteria,the Archaea,and the Eukaryotes had to take its place.At first,phylogeny trees based on differences in the amino acid sequences,then among ribosomal RNAs and also nuclear gene from hundreds of microbial species were depicted and many mini phylogenetic trees grouped the species according to their differences in the sequences.It was found that they shared genes between their contemporaries and across the species barriers.At the root of the phylogeny tree,there was not a single common cell,it was replaced by a common ancestral community of primitive cells.Genes transfered rather freely as the transposons swapping between those cells.There was no last universal common ancestor of single cell that could be found in the revised Tree of Life,It was not easy to represent the genealogical patterns of thousands of different families of genes,in one systematic map,therefor there was no trunk at all.