直系同源与旁系同源

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所属分类:Glossary

Homologous sequences.

Orthologs and Paralogs are two types of homologous sequences. Orthology describes genes in different species that derive from a common ancestor. Orthologous genes may or may not have the same function.Paralogy describes homologous genes within a single species that diverged by gene duplication.

Orthologs 和 Paralogs 是同源序列的两种类型。Orthology描述在不同物种中来自于共同祖先的基因。Orthologous基因可能有相同的功能,也可能没有。Paralogy描述在同一物种内由于基因复制而分离的同源基因。Orthology通常译作直系同源、直向同源、垂直同源。Paralogy通常译作旁系同源、并系同源、横向同源。

NCBI的Glossary中对paralog的定义是: A paralog is one of a set of homologous genes that have diverged from each other as a consequence of gene duplication. For example, the mouse a-globin andb-globin genes are paralogsThe relationship between mouse a-globin and chick b-globin is also considered paralogous (see the figure).

直系同源与旁系同源

即,祖先基因经过复制后分离产生的基因是paralog,例如鼠的a球蛋白和b球蛋白基因。并且,鼠的a球蛋白和鸡的b球蛋白基因的关系也是paralog。

因此不能说:来自不同物种的就不是paralog。这一点就与前面的定义不一致了,前面说:“Paralogy describes homologous genes within a single species that diverged by gene duplication.”

NCBI的Glossary中对ortholog的定义是: Orthology describes genes in different species that derive from a single ancestral gene in the last common ancestor of the respective species.

即,Orthology 指的是这样一些基因,它们起源于这些基因所在物种的最近的共同祖先的一条基因。

TRENDS in Genetics Vol.18 No.12 December 2002 的一篇文章:《Orthology, paralogy and proposed classification for paralog subtypes》对两者的定义做了进一步的探究。作者指出:

Paralogs are defined as genes that derive from a single gene that was duplicated within a genome.The latter definition does not specify that paralogs can only be found in a single organism, and hence genes in different organisms that arose from gene duplication in an ancestral genome are also paralogs according to the definition。

作者根据复制事件与物种分化事件发生的先后关系,提出了inparalog和outparalog的概念,对于一个给定的世系,在物种分化后发生复制事件产生的基因称为inparalog,而复制事件在分化之前,则称为outparalog。

 As we know ,there are two kinds of homolog, ortholog and paralog. Genes in two  species that have directly evolved from a single gene in the last common ancestor are called orthologs. A set of homologous genes that have diverged from each other as a consequence of genetic duplication are called paralogs. Sometime those paralogs which arose from a duplication after the speciation event are called in-paralogs.

文献下载:http://www.sciencedirect.com/science/article/pii/S0168952502027932

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    • avatar LeonNY 1

      分析的很好,学习了