恶人谷

森林的火焰 wrote:作者好象以为基因突变是流感一样，隔一段时间爆发一次似的。

It is important to stress that such estimates of TMRCAs do not imply that the human population contained only one woman at 230 kya (the time of the mtDNA-based TMRCA, assuming constant mutation rates) or only one man at 100 kya (the time of the NRY-based TMRCA). The only implication is that all human mitochondria existing today descend from that of a single woman living 230 kya, and all NRYs descend from that of a single man living 100 kya. In both cases, it is likely that there were many more human individuals alive at the TMRCA—whether they were of the same species as Homo sapiens is hard to determine, but descendants of other species are either absent or extremely rare.

Although the reconstructed genealogies of mtDNA and NRY are broadly similar, there are some notable differences, probably owing to social differences in migration customs. For example, patrilocal marriage has historically been more common than matrilocal84, which can explain differences in mtDNA and Y chromosome data in a number of populations85, 86, 87, 88, 89, 90, 91, 92, 93. Demographic differences between the sexes, such as greater male than female mortality, the greater variance in reproductive success of males than females and possibly the greater frequency of polygyny than polyandry, may explain the discrepancy between the NRY and mtDNA dates. These factors reduce the effective number of males and may explain the more than twofold difference between the NRY-based and the mtDNA-based TMRCA. Another attractive alternative explanation is that mutation rates in mtDNA are very variable, and when this variation is taken into account TMRCA of mtDNA could become closer to that of NRY.

Estimates of TMRCAs from autosomal genes are higher than those from mtDNA or NRY. In theory, they should be higher by a factor of four and the estimates are in this direction, although the number of autosomal genes studied is small and estimates of TMRCAs vary considerably94. For analyses of autosomal and X chromosomes, recombination can complicate genealogies and make TMRCAs impossible to estimate. There is also the possibility of heterozygote advantage, which has the potential to increase estimates of TMRCA. Heterozygote advantage may be widespread throughout the human genome but has been very difficult to show unequivocally, and the only fully confirmed example is sickle cell anemia, for which very large samples were required. There is some optimism, however, that the development of techniques that can detect heterosis for some genes in yeast95 may lead to greater success in other organisms, including humans.

狸狸 wrote:开始几贴看得有些羞赧……然后发现火焰也露了怯 ，小K也8懂 ，就重新兴奋起来
张爱玲的谈读书还是谈读书2里，也有长篇大论讨论种族迁徙的段落，当时我也是看得津津有味。不过不记得那是她几时写的，依据的是哪段时间的研究成果，只觉得被她一写非常有意思。
人们群众还是中意斩钉截铁的结论啊，挖掘自己内心深处对“信我者得永生”的渴望ing

Jun wrote:因为精子不带细胞质, 只带细胞核, 所以受精卵中的线粒体都是从母亲那里来的). 所以不受父亲基因的影响

tiffany wrote:看，这就是为哈地球上恁多人口，都是打一个夏娃传下来的原因啊！

Jun wrote: ..
用Y染色体和mtDNA来追溯geneaology, 就是因为它们的一传到底的特点, 父传子, 或者母传女传女传女... 不会被父母双方的染色体混合打乱规律, 每一代都重新洗牌.