染色体尺度重组率的双参数表征
Two-Parameter Characterization of Chromosome-Scale Recombination Rate
摘要：
一个物种的全基因组重组率（$RR$）通常用一个参数来描述，即总遗传图谱长度（$G$）与物理图谱长度（$P$）之间的比值，以厘米摩根/兆碱基（cM/Mb）为单位测量。该参数的值在物种之间变化很大，但这些差异的原因尚不完全清楚。一个物种中总$RR$的一个限制因素，可能导致较小染色体的$RR$增加，是每个染色体（或染色体臂）每次减数分裂至少需要一个交叉。在本研究中，我们通过线性回归模型量化了较小染色体上重组事件的相对过量，该模型将染色体的遗传长度与其物理长度相关联。我们发现几个物种的双参数回归，$G= G_0 + k \cdot P$提供了一个更好的表征遗传和物理图谱长度之间的关系比单参数回归，贯穿原点。非零截距（$G_0$）表示基因组中较小染色体上的重组相对过量。给定$G_0$，参数$k$预测遗传图谱长度的增加超过物理图谱长度的增加。不同物种的$G_0$的观测值具有相似的幅度，而$k$变化两个数量级。这种策略的影响，人类，小鼠，大鼠，鸡，蜜蜂，蠕虫和酵母的遗传图谱进行了讨论。
英文摘要：
The genome-wide recombination rate ($RR$) of a species is often described by one parameter, the ratio between total genetic map length ($G$) and physical map length ($P$), measured in centiMorgans per Megabase (cM/Mb). The value of this parameter varies greatly between species, but the cause for these differences is not entirely clear. A constraining factor of overall $RR$ in a species, which may cause increased $RR$ for smaller chromosomes, is the requirement of at least one chiasma per chromosome (or chromosome-arm) per meiosis. In the present study, we quantify the relative excess of recombination events on smaller chromosomes by a linear regression model, which relates the genetic length of chromosomes to their physical length. We find for several species that the two-parameter regression, $G= G_0 + k \cdot P$ provides a better characterization of the relationship between genetic and physical map length than the one-parameter regression that runs through the origin. A non-zero intercept ($G_0$) indicates a relative excess of recombination on smaller chromosomes in a genome. Given $G_0$, the parameter $k$ predicts the increase of genetic map length over the increase of physical map length. The observed values of $G_0$ have a similar magnitude for diverse species, whereas $k$ varies by two orders of magnitude. The implications of this strategy for the genetic maps of human, mouse, rat, chicken, honeybee, worm and yeast are discussed.
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