The genomic proportion that two relatives share identically by descent-their genetic relatedness-can vary depending on the history of recombination and segregation in their pedigree. Previous calculations of the variance of genetic relatedness have defined genetic relatedness as the proportion of total genetic map length (cM) shared by relatives, and have neglected crossover interference and sex differences in recombination. Here, we consider genetic relatedness as the proportion of the total physical genome (bp) shared by relatives, and calculate its variance for general pedigree relationships, making no assumptions about the recombination process. For the relationships of grandparent-grandoffspring and siblings, the variance of genetic relatedness is a simple decreasing function of r̄, the average proportion of locus pairs that recombine in meiosis. For general pedigree relationships, the variance of genetic relatedness is a function of metrics analogous to r̄ Therefore, features of the aggregate recombination process that affect r̄ and analogs also affect variance in genetic relatedness. Such features include the number of chromosomes and heterogeneity in their size, the number of crossovers and their spatial organization along chromosomes, and sex differences in recombination. Our calculations help to explain several recent observations about variance in genetic relatedness, including that it is reduced by crossover interference (which is known to increase r̄). Our methods further allow us to calculate the neutral variance of ancestry among F2s in a hybrid cross, enabling precise statistical inference in F2-based tests for various kinds of selection.

中文翻译：

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遗传相关性的变化是由聚集重组过程决定的。

两个亲属在血统上具有相同的基因组比例（他们的遗传相关性）可能会根据其谱系中重组和分离的历史而变化。先前对遗传相关性方差的计算将遗传相关性定义为亲属共享的总遗传图谱长度（cM）的比例，并且忽略了交叉干扰和重组中的性别差异。在这里，我们将遗传相关性视为亲属共享的总物理基因组（bp）的比例，并计算其一般谱系关系的方差，不对重组过程做出任何假设。对于祖孙和兄弟姐妹的关系，遗传相关性的方差是r̄的简单递减函数，r̄ 是减数分裂中重组的基因座对的平均比例。对于一般谱系关系，遗传相关性的方差是类似于r̄的度量的函数，因此，影响r̄和类似物的聚合重组过程的特征也会影响遗传相关性的方差。这些特征包括染色体的数量及其大小的异质性、交叉的数量及其沿染色体的空间组织，以及重组中的性别差异。我们的计算有助于解释最近关于遗传相关性方差的一些观察结果，包括它因交叉干扰而减少（已知会增加r̄）。我们的方法进一步使我们能够计算杂交中 F2 之间祖先的中性方差，从而能够在基于 F2 的测试中对各种选择进行精确的统计推断。