什么是selective sweep?

  • A+
所属分类:Glossary

最近看到的几篇涉及进化的文章里面都提到selective sweep,特地对这个词进行了了解,搜到了一些资料与大家分享一下。

先贴上维基百科上的介绍:

A selective sweep is the reduction or elimination of variation among the nucleotides in neighboring DNA of a mutation as the result of recent and strong positive natural selection.

A selective sweep can occur when a new mutation occurs that increases the fitness of the carrier relative to other members of the population. Natural selection will favour individuals that have a higher fitness and with time the newly mutated variant (allele) will increase in frequency relative to other alleles. As its prevalence increases, neutral and nearly neutral genetic variation linked to the new mutation will also become more prevalent. This phenomenon is called genetic hitchhiking. A strong selective sweep results in a region of the genome where the positively selected haplotype (the mutated allele and its neighbours) is essentially the only one that exists in the population, resulting in a large reduction of the total genetic variation in that chromosome region.

个人感觉上的英文读起来,不是很贴切;下面列举丁香园网友的介绍:

回答一:

selective sweep说的意思就是由于某一位点受到强选择后,其周围的位点的多态性因受改位点牵连而发生多态性降低的现象。

可以这样理解:某个位点发生突变,突变后的位点因对物种在特定的情况下有利或者受到了人为的选择,那么该突变位点在群体中的频率必然提高,但是其附近和它处在同一个单体型或者block的其他的多态位点同样跟着受到了选择,频率发生了提高,也就是该单体型内的其他多态位点的某一多态形式比率大大提高,从而降低了整个周围区域的多态性。

举个简单的例子(不切实际):假如高个子和黑头发在同一个block内,共遗传。但是还存在其他的共遗传及矮个子黄头发,矮个子蓝头发,矮个子白头发。这时头发颜色这一多态性很高,但是有一天,女生只爱高个子的男生,但她们不关心你是什么头发,这样,高个子首先被选择,和他连锁在一起的黑头发就变向的受选择,这样后代里大部分就是高个子黑头发了,这样头发颜色的多态性大大下降。这就是发生了selective sweep。

所以Sweep是因为受牵连而发生的,与疾病也有关系,很有名的例子,疟疾和镰刀状贫血病就是这样的一个过程。

回答二:

周围位点是处于同一个haplotype内的SNP位点。比如说:A1、B1、C1三个SNP位点处在同一个haplotype内,其它的haplotype有A3B2C2、A2B1C2、A4b3C3等等,若A1受选择,那么A1B1C1这种单体型频率将提高,这样因受牵连,B1C1的频率也大大提高,而群体中B2、B3、C2、C3的频率就相对下降,如果是强选择,他们甚至可能丢失。

其实周围的位点从整体上看频率的改变应该是一个近似钟形分布,也就是越靠近受选择位点,频率改变的约剧烈。

至于是物理距离还是遗传距离就说不清了,应为他们的单位太大了。

sweep强调的应该是进化上的后果,它是研究物种受选择而进化的一个术语。

最后附上一篇nature上的图片:

selective sweep

A selective sweep

Under natural selection, a new beneficial mutation will rise in frequency (prevalence) in a population. A schematic of polymorphisms along a chromosome, including the selected allele, before and after selection. Ancestral alleles are shown in gray and derived (non-ancestral) alleles are shown in blue. As a new positively selected allele (red) rises to high frequency, nearby linked alleles on the chromosome 'hitchhike' along with it to high frequency, creating a 'selective sweep.'

avatar

发表评论

:?: :razz: :sad: :evil: :!: :smile: :oops: :grin: :eek: :shock: :???: :cool: :lol: :mad: :twisted: :roll: :wink: :idea: :arrow: :neutral: :cry: :mrgreen: