Sex-averaged recombination and mutation rates on the X chromosome: a comment on Labuda et al.
Sex-averaged recombination and mutation rates on the X chromosome: a comment on Labuda et al.
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X 染色体上的性别平均重组率和突变率：Labuda 等人的评论
DOI：
10.1016/j.ajhg.2010.03.021
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发表时间：
2010
影响因子：
9.8
通讯作者：
Keinan,Alon
中科院分区：
文献类型：
--
作者：
Lohmueller,KirkE;Degenhardt,JeremiahD;Keinan,Alon
致编辑：Labuda等人最近发表的一篇论文，利用X染色体和常染色体上的HapMap数据中SNPs之间的连锁不平衡（LD）模式来估计人类群体中女性与男性的繁殖比例（b= Nf/Nm）。我们对这种方法非常感兴趣，因为最近两篇使用SNP多样性和频率模式研究性别偏向人口统计学的论文2,3在X染色体的有效种群大小是否大于预期的结论上存在差异。X染色体上大于预期的有效群体大小可能是由于雌性比雄性有效群体大小大（b >1）。由于之前的研究都没有使用LD模式中包含的信息，Labuda等人的研究1原则上可以提供对b的独立估计。他们发现证据表明b略大于1，但仍小于Hammer等人报告的值。因此，Labuda等人1得出结论，在整个人类历史中，几乎没有证据表明存在一夫多妻制，或者女性比男性更大的有效种群规模。然而，他们的分析推导中的错误影响了他们的大部分分析，对这些错误的修正导致了不同的结论。Labuda et al. 1在推导式4中，通过表达rX=(2b/(1+ 2b)) rfX，指出X染色体的性别平均重组率rX取决于种群的雌雄繁殖比，其中rfX为雌性重组率。然而，rX=(2/3) rfX并且与b无关，因为每个后代都是由雄性雌性交配产生的，而不管种群中的性别比例如何。因此，由于X染色体上的重组只能发生在女性身上（rmX= 0），三条潜在传递的X染色体中只有两条可能是重组事件的产物。种群中繁殖雄性和雌性数量相等的偏差会改变X染色体有效种群大小（NeX）和常染色体（NeA）之间的关系，但不会改变每次交配仍然由单个父本和单个母本组成的事实（图1），保持rX=(2/3) rfX。因此，作者的表述基本上对男女人口规模不等进行了双重修正。正确的表达（rX=(2/3) rfX）已经被推导出来（参见4），也被用来解释果蝇X染色体和常染色体上遗传变异模式的差异
To the Editor: A recent paper by Labuda et al. 1 used patterns of linkage disequilibrium (LD) among SNPs from the HapMap data on the X chromosome and the autosomes to estimate the female-to-male breeding ratio in human populations (b= Nf/Nm). This approach was of considerable interest to us because two recent papers 2, 3 using SNP diversity and frequency patterns to study sexbiased demography differed in their conclusion as to whether the effective population size of the X chromosome was larger than expected. A larger than expected effective population size on the X chromosome could be due to a larger female than male effective population size (b> 1). Because neither of the previous studies used information contained within LD patterns, the study of Labuda et al., 1 in principle, could provide independent estimates of b. They find evidence that b is slightly larger than 1 but still smaller than the value reported by Hammer et al. 2 Thus, Labuda et al. 1 concluded that there is little evidence for polygyny, or a larger female than male effective population size, throughout human history. However, errors in their analytical derivations affect most of their analyses, and correction of these errors leads to different conclusions.In deriving Equation 4, Labuda et al. 1 state that the sexaveraged recombination rate on the X chromosome, rX, depends on the female-to-male breeding ratio of the population through the expression rX=(2b/(1+ 2b)) rfX, in which rfX is the female recombination rate. However, rX=(2/3) rfX and is independent of b because each offspring is produced from a male-female mating, regardless of the sex ratio in the population. Therefore, because recombination on the X chromosome can occur only in females (rmX= 0), only two of the three potentially transmitted X chromosomes can be the product of a recombination event. Deviations from an equal number of breeding males and females in the population will change the relationship between the effective population sizes of the X chromosome (NeX) and the autosomes (NeA), but will not change the fact that each mating will still consist of a single male parent and a single female parent (Figure 1), keeping rX=(2/3) rfX. Thus, the authors’ expression essentially double-corrects for unequal male-female population sizes. The correct expression (rX=(2/3) rfX) has been previously derived (reviewed in 4) and has also been used to interpret differences in patterns of genetic variation on the X chromosome and autosomes in Drosophila. 5, 6 The expression
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