Dissertation Research: Using Patterns of Nucleotide Diversity to Distinguish Between Modes of Selection in Very Low Recombining Regions of the Drosophila Genome

遗传物质通过杂交在母系和父系同源染色体之间交换。一个基因的DNA序列在物种内的变异程度与该基因经历杂交的频率有关。果蝇的4号染色体缺乏杂交，其基因表现出很少的变异。这为检验关于交叉和变异之间关系的两个主要假设提供了机会。根据第一种假设，在没有杂交的情况下，变异被消除了，因为一个选择性有利的变异在整个物种中传播时，会拖着染色体上的所有基因一起传播。可变性的恢复依赖于新的突变，而这必然是罕见的。在第二种假设下，变异减少是因为选择不断地消除染色体上的有害突变；罕见变异和常见变异的相对丰度应该很少受到影响。这些假设将通过使用DNA测序技术检查该染色体上基因的罕见变异和常见变异的比例来验证。这项研究将揭示影响自然种群多样性水平的遗传机制。这对保护生物学和人类变异遗传学以及基本生物过程的知识具有广泛的影响。

9701114 Charlesworth Genetic material is exchanged between maternally and paternally derived homologous chromosomes, by the process of crossing over. The level of within-species variability in the DNA sequence of a gene is related to the frequency with which the gene experiences crossing over. Chromosome four of the fruitfly Drosophila melanogaster lacks crossing over, and its genes show little variability. This provides an opportunity to test two major hypotheses about the relation between crossing over and variability. Under the first hypothesis, variability is eliminated in the absence of crossing over because a selectively favorable variant drags all genes on the chromosome along with it, as it spreads through the species. Restoration of variability depends on new mutations, which are necessarily rare. Under the second hypothesis, variability is reduced because selection continually eliminates harmful mutations all along the chromosome; the relative abundance of rare versus common variants should be little affected. These hypotheses will be tested by examining the proportions of rare versus common variants at genes on this chromosome, using DNA sequencing technology. This research will shed light on the genetic mechanisms affecting diversity levels in natural populations. This has broad implications for conservation biology and the genetics of human variation, as well as for knowledge of fundamental biological processes.