科学杂志：以前认为夫妇血缘远比较好，但冰岛的遗传研究查了165年的家谱和16万对夫妇后发现
第三表亲 （3rd cousin）生的孩子最多，而且孙子也最多。 第一和第二表亲生的多， 但孩子死得早，所以孙子也少。 血缘再远，孩子就少生了。非常重要的是冰岛居民贫富差距不大，移民非常少。 血统纯正，家谱完整， 是做遗传学研究的好地方。
这个研究表明两个血缘太近太远的夫妇婚姻可能对孩子健康不利。我们的孩子要知道这些喔！这是deCODE Genetics 研究的一部分。 这个研究非常有名， 最近刚刚报道冰岛人的基因序列
差不多都被检测出来了（一个家族只需做代表人物），好像找到很多和疾病有关的信息。。。
在中国，第三表亲大概不认识了吧，家谱不完整很难做的。
- Helgason, A. et al. Science 319, 813-816 (2008). | Article | 原文要付钱，无法download。 这是“自然”杂志的新闻报道
http://www.nature.com/news/2008/080207/full/news.2008.562.html
When kissing cousins are good for kids
A little inbreeding might boost fertility.
A bit of genetic familiarity might boost fertility.GettyNo doubt about it: incest has a bad reputation. In Western societies, ‘kissing cousins’ are mocked, reviled and sometimes outlawed. Oddly, however, a new study suggests that a little bit of inbreeding might be beneficial to the family line.
Researchers combed through 165 years of genealogical records tracing more than 160,000 couples in Iceland. They found that the more closely related that couples were, the more children and grandchildren they tended to have. But for first and second cousins the outlook was gloomy — their offspring died younger and reproduced less.
Breeding outside of the family is considered beneficial because it provides a source of new genetic material. Outbreeding increases the chances that offspring will inherit at least one ‘good’ copy of a gene, potentially masking harmful mutations lurking in a family’s genetic background. Without that influx of fresh genetic material, the probability of birth defects rises: highly inbred animals and royal families are littered with the consequences. Inbreeding is also thought to decrease the reproductive success of offspring.
But the new results suggest that things don't always work that way, says Kári Stefánsson of deCODE Genetics in Reykjavik, and an author on the study. “It’s counterintuitive in many ways,” he says.
It's all relative
Inbreeding once ran rampant in the West, particularly in rural societies where finding a mate outside of the family could entail a long hike to the next village. And first-cousin marriages are common today in many eastern cultures, where marrying within the family is a way to avoid a dowry and consolidate familial resources.
“In Western society there is this impression that inbreeding is bad,” says Alan Bittles, a human geneticist at Edith Cowan University in Perth, Australia. “But that didn’t really commence until the middle of the nineteenth century.”
Researchers have studied the question of how inbreeding weakens the family line for decades. But they have generally struggled to tease out the effects of inbreeding from study groups with vast differences in social and economic status.
Stefánsson and his colleagues tackled the question using data from Iceland, an island about half the size of the United Kingdom with a remarkably homogeneous population in terms of socioeconomic status. The researchers found that first and second cousins had more children than distantly related couples, but that those children also die at a younger age and bear fewer children. That fits with previous data showing that children of first-cousin marriages have a 3-4% higher chance of ill health or early death.
Third and fourth cousins also had more children than more distantly related couples, but their children tended to be more reproductive. For example, women born between 1925 and 1949 who partnered with a third cousin had an average of 3.3 children and 6.6 grandchildren. Women born during the same period who had a partner that was an eighth cousin or more distantly related, had only 2.5 children and 4.9 grandchildren on average.
Live long and prosper
Although the researchers don't have more subtle data on the health of these children, the number of children who go on to have children of their own is often taken as a general marker of 'genetic fitness': they get to pass on their DNA to future generations. In this regard, the third and fourth cousins were best off. The results are published today in Science1.
The result may reflect the fact that genetic compatibility is important to breeding, says Bittles. For example, a dangerous condition called ‘Rh incompatibility’ can arise when one parent has an antigen called the Rh factor and the other doesn't. If the developing fetus inherits the father's Rh status, then it can trigger an immune response in the mother.
There might be a compromise to be struck between the benefits and problems of genetic similarity, says Bittles. “The idea that there could be an optimum balance makes sense,” he says.
Corrected:
This article originally stated that Ireland was larger than the United Kingdom; this has been corrected.-
References
- Helgason, A. et al. Science 319, 813-816 (2008). | Article |
