Molecular Evolution of X-Y Meiotic Drive in Drosophila

描述（申请人提供）中斑果蝇的自然种群具有X染色体（称为性比，或“SR”），因此XSRY雄性果蝇不产生携带Y染色体的精子。由此产生的偏向女性的性别比例可能会导致人口灭绝。然而，这些群体也具有Y染色体，其是SR表达的抑制子，使得XSRY抑制子产生相等数量的儿子和女儿。该系统是研究Y染色体和自私遗传元件群体遗传学的一个很好的实验模型。人群具有稳定的非中性Y多态性（Y抑制/ Y非抑制），这在理论上是出乎意料的。我们将做进一步的实地收集，以测试提出的假设，稳定这种多态性。最近对果蝇Y染色体上的三个动力蛋白基因的表征使我们能够量化果蝇Y染色体的多态性水平和共同祖先的日期。中斑的。XSR和Y抑制染色体分布广泛，不知道它们是出现一次（然后扩散）还是出现多次。这个问题对于评估自私基因的进化意义至关重要：自私基因的重复起源表明它们是一种常见的威胁，而单一起源意味着一旦自私基因通过突变产生，它就能够入侵一个物种的所有种群。我们将通过使用DNA序列的系统发育研究来回答这个问题：如果来自遥远人群的抑制Y染色体形成一个簇（与非抑制Y分开），那么它们有一个单一的起源。类似的推理适用于XSR染色体。DNA序列也将被用来估计这些自私基因的年龄，使用基于分子钟的分析方法。

DESCRIPTION (provided by applicant)Natural populations of Drosophila mediopunctata harbor X chromosomes (called sex-ratio, or "SR") such that XSRY males produce no Y-bearing sperm. The resulting female-biased sex ratio can be driven to the point of population extinction. However, these populations also have Y chromosomes that are suppressors of SR expression, such that XSRY suppressor produce equal numbers of sons and daughters. This system is an excellent experimental model to study the population genetics of Y chromosomes and selfish genetic elements. The populations have a stable, non-neutral Y-polymorphism (Y supressor / Y non-suppressor) which is unexpected on theoretical grounds. We will do further field collections to test a proposed hypothesis of stabilization of this polymorphism. Recent characterization of three dynein genes on the Drosophila Y chromosome allows us to quantify levels of polymorphism and dates of common ancestry of Y chromosomes of D. mediopunctata. XSR and Y suppressor chromosomes are widespread, and it is not known whether they appeared once (and then spread) or whether they appeared several times. This question is fundamental to evaluate the evolutionary significance of selfish genes: repeated origins of selfish genes suggest that they are a frequent threat, whereas a single origin implies that once a selfish gene arises by mutation, it is able to invade all populations of a species. We will answer this question by phylogenetic studies using DNA sequences: if suppressor Y chromosomes from distant populations form a cluster (separated from non-suppressor Y), then they had a single origin. An analogous reasoning applies to the XSR chromosomes. DNA sequences will also be used to estimate the age of these selfish genes, using analytical methods based on the molecular clock.