Rates of DNA Sequence Change on Avian Chromosomes: A Test of the Replicative Division Hypothesis

DNA或蛋白质序列随时间以稳定的速率变化的证据在20世纪60年代初提出，现在包括使用序列差异量来估计物种对多久以前彼此分化的基本原理。 这被称为“分子钟”。 这一比率究竟有多稳定一直是一个有相当大争议的问题。 特别是，最近人们对决定时钟“滴答”的速率的“马达”感兴趣。 一种假设是DNA突变主要发生在复制过程中，并且速率由生殖系细胞谱系在每单位时间内遇到的复制轮数决定。 例如，这可以解释为什么老鼠在序列水平上比人类进化得更快。 如果这个假设是正确的，那么主要通过雄性或主要通过雌性脊椎动物谱系传递的染色体中的DNA应该以不同的速度进化，因为雌性在配子产生中使用的复制轮数比雄性少。 虽然在哺乳动物中观察到了这种趋势，但对这一结果的含义可能有其他解释。 在这项研究中，托马斯W.奎因将比较鸟类W、Z和常染色体内的DNA序列变化率。 分子技术将用于鉴定和测序在W和至少一条其他染色体上发现的可比DNA序列。 将测量这些序列的变化率，并与预测结果进行比较，W染色体上的序列将显示比其他染色体上的可比序列更少的变化。 这是对哺乳动物研究的一个重要补充，因为鸟类中存在雌性特异性染色体，而不是哺乳动物中的雄性特异性染色体。 鸟类研究系统提供了一个机会，以测试的假设的DNA突变率的DNA复制频率的依赖性，在不同的染色体之间的速率差异的情况下，预测是不同的方向和幅度从哺乳动物染色体上发现的。

9629462 QUINN Evidence that DNA or protein sequences change at a steady rate through time was presented in the early 1960s, and now comprises the rationale for using amounts of sequence divergence to estimate how long ago species pairs diverged from each other. This has become known as the "molecular clock". Just how steady that rate is has been a matter of considerable debate. In particular, there has been recent interest in what the "motor" is that determines the rate at which the clock "ticks". One hypothesis is that DNA mutation occurs primarily during replication and that the rate is determined by number of rounds of replication encountered by germ line cell lineages per unit of time. This may explain why, for instance, mice evolve more quickly than humans at the sequence level. If this hypothesis is correct, then DNA within chromosomes that are passed on primarily through male or primarily through female vertebrate lineages should evolve at different rates because females use fewer numbers of rounds of replication in the production of gametes than do males. While this trend has been observed in mammals, other interpretations of the meaning of this result are possible. In this study, Thomas W. Quinn will compare rates of DNA sequence change within the W, Z and autosomal chromosomes in birds. Molecular techniques will be used to identify and sequence comparable DNA sequences found on the W and at least one other chromosome. The rate of change in these sequences will be measured and compared with the predicted result, that sequences on the W chromosome will show fewer changes than comparable sequences on other chromosomes. This is an important addition to mammalian studies because there is a female-specific chromosome in birds rather than a male-specific chromosome as in mammals. The bird study system presents an opportunity to test the hypothesis of the dependence of DNA mutation rate on frequency of DNA replication, in a case where rate differences between various chromosomes are predicted to be different in direction and magnitude from those found on mammalian chromosomes.