Evolution of Dimorphic Sex Chromosomes

拟议中的研究将通过实验测试预测 根据最近的理论，关于导致 二态性染色体的进化 大多数动物， 一小部分植物物种，有一对特殊的 染色体，X和Y性染色体，决定性别。 典型的模式是雄性携带两种性别 染色体，X和Y，并为女性携带两个 性染色体的类型（X）。 现在有几条证据 表明性染色体来自于一对 以前与染色体无关的染色体 性别的决定。 这种转变首先涉及到 一个主要的性别决定基因的进化，其次是 决定性别的染色体片段的进化，最后 在性别决定染色体的进化中。 期间 性染色体的进化，其中一条染色体，X， 增强的生物化学活性（剂量补偿）， 伴侣染色体，Y，被降解，几乎失去了所有的 遗传活动。 性染色体也失去了 在这个转变过程中交换遗传物质。 一个 了解负责的遗传机制， 性染色体的形成是建议的重点 research. 研究人员将使用一个果蝇 （普通果蝇）模型系统，以实验方式创建一种新的 一对决定性别的基因和染色体。 研究者 然后将使用这个模型系统来探索 导致两性间基因交换的中断 染色体，以及导致退化的机制， Y性别的遗传活性（突变的积累） 染色体 对两性异形进化的认识 染色体有许多实际应用。 第一，存在 性染色体的突变导致雄性（更普遍的是异配子 更容易患遗传性疾病。 二形 性染色体是性连锁遗传的物质基础 并导致男性遗传许多遗传性疾病 比女性多一倍。 二态性的演化 性染色体也导致剂量现象 补偿（基因表达水平的改变， 位于性染色体上的遗传物质）。 生化 剂量补偿的不规则性导致了一些 遗传性疾病的形式。 拟议的实验还将 监测有害突变在两性之间的累积 染色体和普通染色体上。 了解 这个积累过程对于理解风险 暴露水平不断增加的人群， 辐射（例如，从核废料和稀释产生的辐射） 大气层的臭氧层）。 最近应用 研究人员的理论工作还表明， 这些实验将有助于确定遗传风险 (due近亲繁殖的衰退和自然的背景水平 辐射）对野生动物种群的影响， 有效种群规模，如公园和游戏中发生的情况 避难所

The proposed research will experimentally test predictions from recent theory, concerning the mechanisms that lead to the evolution of dimorphic sex chromosomes. Most animal species, and a smaller percentage of plant species, have a special pair of chromosomes, the X and Y sex chromosomes, that determine gender. The typical pattern is for males to carry two types of sex chromosomes, and X and a Y, and for females to carry two of the same type (X) of sex chromosome. Several lines of evidence now indicate that sex chromosomes are derived from a pair of chromosomes which formerly were not associated with the determination of gender. This transition first involves the evolution of a major sex determining gene, followed by the evolution of a sex-determining chromosomal segment, and finally in the evolution of sex-determining chromosomes. During the evolution of sex chromosomes, one chromosome, the X, evolves enhanced biochemical activity (dosage compensation) while the partner chromosome, the Y, is degraded and loses virtually all genetic activity. The sex chromosomes also lose their ability to exchange genetic material during this transition. An understanding of the genetic mechanisms responsible for the formation of sex chromosomes is the focus of the proposed research. The investigator will use a Drosophila melanogaster (common fruit fly) model system to experimentally create a new pair of sex- determining genes and chromosomes. The investigator will then use this model system to explore the mechanisms that lead to the breakdown in genetic exchange between the sex chromosomes, and to the mechanisms that lead to the deterioration (accumulation of mutations) of the genetic activity of the Y sex chromosome. An understanding of the evolution of dimorphic sex chromosomes has many practical applications. First, the presence of sex chromosomes causes males (more generally the heterogametic sex) to be far more susceptible to hereditary disease. Dimorphic sex chromosomes are the physical basis for sex-linked inheritance and cause males to inherit many hereditary diseases thousands of times more frequently than females. The evolution of dimorphic sex chromosomes also results in the phenomena of dosage compensation (a modified level of gene expression for the hereditary material located on the sex chromosomes). Biochemical irregularities with dosage compensation are responsible for some forms of hereditary disease. The proposed experiments will also monitor the accumulation of deleterious mutations on both the sex chromosomes and on ordinary chromosomes. An understanding of this accumulation process is important in understanding the risk to human populations of increasing levels of exposure to radiation (e.g. that produced from nuclear waste and the thinning of the ozone layer of the atmosphere). Recent applied theoretical work by the investigator also suggests that data from the experiments will be useful in determining the genetic risk (due to inbreeding depression and natural levels of background radiation) to wildlife populations that are maintained to small effective population size, such as occurs in parks and game refuges.