美研究称同一个人的精子间亦存巨大DNA差异
[i=s] 本帖最后由 sunsong7 于 2012-7-23 16:15 编辑 [/i][table=98%,#f8f9f4]
[tr][td][align=left][float=left]作者：孝文 来源：新浪科技 发布时间：2012-7-23 14:57:45[/float]
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[tr][td]美研究称同一个人的精子间亦存巨大DNA差异[/td][/tr]
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[align=center][img]http://news.sciencenet.cn/upload/news/images/2012/7/20127231452451760.jpg[/img][/align][align=center][font=楷体_GB2312]一项新研究显示，即使来自同一个人的精细胞，也存在巨大遗传差异。[/font][/align]北京时间7月23日消息，人类精子争夺卵子的“比赛”看起来就像一群蝌蚪在争先恐后地蠕动，但哪一个精子获胜，结果是大不一样的。一项新研究显示，即使是来自同一个人的精子细胞，也存在显著的遗传差异。
科学家首次获得了来自同一个人的近100个精子的基因图谱。这些结果确认了科学家早已知道的一个事实：每个精子都是不同的，因为它们遗传DNA的方式变化多端。这些称作重组的过程混合了从一个人的父母那里遗传而来的基因，增加了遗传多样性。
科学家研究了来自同一个人的91个精子，结果发现每个精子平均重组或再结合23次。个体精子在这个过程中发生很大变化，经历自发性基因突变。每个精子包含在其他体细胞中看不到的25到36个新突变。
科学家发现2个精子失去全部染色体。随机突变导致遗传变异，如果发生在错误的地点就会有害。一名40岁男子捐赠了这些精细胞，他拥有健康后代和功能正常的精子。
美国加利福尼亚州斯坦福大学的巴里·贝尔教授表示：“我们首次产生了一个人的基因重组图以及一个人数个精子的突变率。现在我们可以着眼于一个特定个人，通过研究他的精子，了解它们产生胚胎的可能性，甚至诊断或检测潜在问题。基因测序或许能提供一个新的早期检测系统，以便确认有生育障碍的男性。”
《细胞》杂志19日发表了这项研究结果。人体的大多数细胞都有两个副本，每个副本含有23对含有从父母那里遗传来的DNA的染色体。但男人的精子和女人的卵子只有一个副本。重组出现在染色体分裂前。在一个称为减数分裂的过程中，数对染色体沿着细胞的中央部分排成一行。然后，部分染色体组可能随机交换，混合遗传DNA的成分。
这个过程产生的遗传变异要比只把完整染色体分离进生殖细胞时产生的遗传变异多。这能有助于确保婴儿从父母以及祖父母那里遗传DNA混合体。
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It DOES make a difference which wins the race: Scientists scan 100 sperm from one man - and find huge DNA differences
By [url=http://www.dailymail.co.uk/home/search.html?s=&authornamef=Rob+Waugh][color=#0066cc]Rob Waugh[/color][/url]
[b]PUBLISHED:[/b] 16:18 GMT, 19 July 2012 | [b]UPDATED:[/b] 11:26 GMT, 20 July 2012
[size=2]The 'race' betweeen human sperm to the eggs might just look like a bunch of wriggling tadpoles - but it makes a big difference which sperm wins.
Even sperm cells from the same man have big genetic differences, a study has shown.
For the first time, scientists have obtained genetic blueprints of almost 100 sperm from a single individual.
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[size=5][img=468,286]http://i.dailymail.co.uk/i/pix/2012/07/19/article-0-1420CDA0000005DC-595_468x286.jpg[/img][/size] [align=left]First place! Even sperm cells from the same man have big genetic differences, a study has shown[/align]
[size=2]The results confirm what scientists already know, that every sperm is different because of the way their inherited DNA is shuffled.[/size]
The process, known as recombination, mixes up genes passed down by a man's mother and father and increases genetic diversity.
Each of the 91 sperm studied showed an average of 23 recombination, or mixing, events. But individual sperm varied greatly in the way they experienced spontaneous genetic mutations.
Every sperm contained between 25 and 36 ‘new’ mutations, not seen in other body cells.
[color=#ff660]For the first time we were able to generate an individual recombination map and mutation rate for each of several sperm from one person,’ said Professor Behr[/color]
Two sperm were found to be missing entire chromosomes, the protein-bound packages of DNA that contain the genes.
Random mutations create genetic variation, but can be harmful if they occur in the wrong places.
The cells were donated by a 40-year-old man who has healthy offspring and normally functioning sperm.
For the first time we were able to generate an individual recombination map and mutation rate for each of several sperm from one person,’ said Professor Barry Behr, from Stanford University in California, US.
Now we can look at a particular individual, make some calls about what they would likely contribute genetically to an embryo, and perhaps even diagnose or detect potential problems.’
Genetically sequencing sperm could provide a ‘new kind of early detection system’ to identify men who may have trouble conceiving, he added.
The research is published today in the journal Cell.
Most cells in the human body have two copies each of 23 chromosomes, containing DNA inherited from both parents. However, sperm in men and eggs in women only have single copies.
Recombination occurs before the chromosomes are partitioned. During a process called meiosis, pairs of chromosomes line up along the midsection of the cell. Portions of the chromosome pairs may then be randomly swapped, mixing up the inherited DNA elements.
This generates much more genetic variation than would be possible if only intact chromosomes were segregated into reproductive cells. It helps ensure that a baby inherits a blend of DNA from all four of his or her grandparents.
Sperm and egg chromosomes pair up to produce the usual two-copy compliment after fertilisation.
[url=http://www.dailymail.co.uk/sciencetech/article-2176016/It-DOES-make-difference-wins-race-Scientists-scan-100-sperm-man--huge-DNA-differences.html]http://www.dailymail.co.uk/sciencetech/article-2176016/It-DOES-make-difference-wins-race-Scientists-scan-100-sperm-man--huge-DNA-differences.html[/url]
个体精子在这个过程中发生很大变化，经历自发性基因突变。每个精子包含在其他体细胞中看不到的25到36个新突变。
突变这么容易发生？不大可能吧？ 这个不奇怪。因为人的精子的基因组是父本和母本基因组的重组形成的。每次分裂时都要经过同源基因的交换。其结果是，“天下没有一个基因组完全相同的精子"! 打破这一规律的可能是近郊系的动物，因为所有的同源基因序列是相同的，没有父本和母本的差别。但是，这也不是100%！估计还是无法打破。
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