Dissecting the genetic basis of selfish sex chromosomes

性别比(SR)染色体是破坏Y染色体传递的X染色体变体， 扭曲后代的性别比例，以牺牲身体健康为代价获得进化优势。高级公务员 染色体在X连锁的畸变子、Y连锁的靶标和一系列 常染色体抑制子。这种进化的军备竞赛为减数分裂的性染色体提供了强有力的解释 性染色体的失活、更替和性别决定系统的进化。SR染色体是 被认为是针对在退化的Y染色体上发现的卫星重复和异染色区，但非常 人们对扭曲的具体遗传基础或分子机制知之甚少。这是因为SR 系统主要是从非模式生物中得知的，通常与复杂的基因组结合在一起 重新安排。在没有描述潜在的遗传基础和分子机制的情况下，它仍然存在 不可能将自私因素引发的军备竞赛与进化中更广泛的现象直接联系起来 减数分裂和性染色体系统。我开发了两个独立的方法来规避 染色体倒置的混淆效应并剖析这种自私的遗传基础 近缘果蝇物种的行为。 具体目标1：开发一种突变方法来识别导致性别比扭曲的基因 在假黑斑潜蝇中。通过对SR染色体的饱和诱变，我鉴定了X连锁的基因 通过屏蔽以减少传输，从而导致失真。迄今为止，已筛选了5,000行(95% 饱和度)，其中33条线路表现出较小的失真。使用CRISPR-Cas9基因组编辑，我建议测试 得到候选基因座的充要条件，并将它们放入一条功能路径中 SR失真。具体目标2：设计一种人工染色体倒置以实现重组 拟青海松毛虫性别比扭曲的定位。此方法适用于特定于FLP/FRT站点 重组工具，以生成完全共线的非驱动染色体，以允许在 包含所有必需且充分的SR扭曲基因的区域。一旦候选基因被绘制出来， 对这两个系统进行了验证，并组织成一个功能途径，对这两个系统进行了比较分析 将测试SR机制是唯一的还是共享的。这两种方法加在一起将提供最大的 到目前为止，性别连锁分离扭曲者的完整遗传结构，打开了理解 两个物种扭曲的分子机制，并首次明确测试了这两个物种的进化 守恒假说和性别比扭曲由以下因素决定的群体遗传学假说 上位性相互作用的X连锁基因通过染色体倒置结合在一起。拟议的研究 提供基因组分析和基因工程方面的培训机会，并奠定坚实的基础 为我的持续研究计划，剖析自私性染色体的进化和细胞基础。

Sex-Ratio (SR) chromosomes are X chromosome variants that subvert the transmission of Y chromosomes, distort the sex ratio of progeny and gain an evolutionary advantage at a cost to organismal fitness. SR chromosomes initiate intense genetic conflict between X-linked distorters, Y-linked targets, and an array of autosomal suppressors. This evolutionary arms race provides a powerful explanation of meiotic sex chromosome inactivation, turnover of sex chromosomes, and evolution of sex determination systems. SR chromosomes are thought to target satellite repeats and heterochromatic regions found on degenerate Y chromosomes, yet very little is known about the specific genetic basis or molecular mechanisms of distortion. This is because SR systems are primarily known from non-model organisms and are often bound up in complex genomic rearrangements. Without characterizing the underlying genetic basis and molecular mechanisms it remains impossible to directly connect the arms race initiated by selfish elements to broader phenomena in the evolution of meiosis and sex chromosome systems. I develop two independent methods to circumvent the confounding effects of chromosomal inversions and dissect the genetic basis underlying this selfish behavior in closely related Drosophila species. Specific Aim 1: Developing a mutagenesis approach to identify the genes causing Sex-Ratio distortion in D. pseudoobscura. Through saturation mutagenesis of SR chromosomes, I identify X-linked of genes contributing to distortion by screening for reduced transmission. To date, >5,000 lines have been screened (95% saturation), with 33 lines exhibiting reduced distortion. Using CRISPR-Cas9 genome editing, I propose to test the necessary and sufficient conditions of resulting candidate loci and place them into a functional pathway for SR distortion. Specific Aim 2: Engineering a synthetic chromosomal inversion to allow recombination mapping of Sex-Ratio distortion in D. persimilis. This approach adapts the Flp/FRT site-specific recombination tools to generate a perfectly collinear non-driving chromosome to allow free recombination in the region containing all necessary and sufficient genes for SR distortion. Once candidate genes are mapped, validated, and organized into a functional pathway for D. persimilis, a comparative analysis of these two systems will test whether SR mechanisms are unique or shared. Together, these two methods will provide the most complete genetic architecture of sex-linked segregation distorters to date, open the door to understanding the molecular mechanisms of distortion in two species, and for the first time explicitly test both the evolutionary conservation hypothesis and the population genetic hypothesis that Sex-Ratio distortion is determined by epistatically interacting X-linked genes bound together by chromosomal inversions. The proposed research provides training opportunities in both genomic analyses and genetic engineering, and establishes a strong basis for my continuing research program dissecting the evolutionary and cellular basis of selfish sex chromosomes.