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

Quinn提出的研究将调查鸟类性染色体和常染色体的单拷贝DNA分化率。繁殖分裂假说认为生殖系细胞每单位时间内的繁殖分裂轮数决定了DNA序列变化的速率。鸟类为验证这一有趣的假设提供了一个极好的模型，因为鸟类的异配子性与哺乳动物的相反。利用禽类染色体中期扩散的显微解剖和DNA扩增与克隆技术，从几种水禽的W、Z和常染色体中分离出单拷贝DNA，并确定这些克隆的核苷酸序列。这些数据将用于比较不同染色体类型的比率与特定染色体经历的复制分裂数量的关系。复制分裂假说和修复机制假说解决了DNA中可遗传突变变化的基本模式。不幸的是，这些假设不能用哺乳动物的染色体来检验。本研究利用一些精心设计的实验程序，一个合适的模型系统（鸟类），以及最新的染色体和分子技术，为这两种相反的假设提供了有力的测试。研究结果有几个含义。首先，获得性别特异性标记，这些标记可用于不表现性别二态性的濒危物种的育种计划。其次，W染色体变化率的结果可以与现有的母体遗传mtDNA序列信息进行比较，这些数据可能对系统生物学具有重要意义。最后，一些非常重要的分子技术将得到完善，这些将为其他比较染色体作图的研究提供巨大的潜力。＊＊＊

9306823 Quinn The proposed research will investigate the rate of single copy DNA divergence in the sex and autosomal chromosomes of birds. The replicative division hypothesis suggests that the number of rounds of replicative division in germ line cells per unit chronological time determines the rate of DNA sequence change. Birds provide an excellent model for testing this interesting hypothesis because in birds the heterogametic sex is reversed from that seen in mammals. Microdissection of avian chromosome metaphase spreads and DNA amplification and cloning techniques will be used to isolate single copy DNA from the W, Z, and autosomal chromosomes of several waterfowl, and the nucleotide sequence of these clones will be determined. These data will be used to compare rates on different chromosome type in relation to the number of replicative divisions that particular chromosome undergoes. %%% The replicative division hypothesis and the repair mechanism hypothesis address the basic pattern of heritable mutational change in DNA. Unfortunately, these hypotheses cannot be tested using mammalian chromosomes. This proposal utilizes some well designed experimental procedures, an appropriate model system (birds), and state of the art chromosome and molecular techniques to provide a powerful test for these two opposing hypotheses. The results have several implications. First, sex specific markers will be obtained, and these markers can be used in breeding programs of endangered species that do not show sexual dimorphism. Second, the results of W chromosome rates of change can be compared to existing information on maternally inherited mtDNA sequences, and these data may have important implications to systematic biology. Finally, some very important molecular techniques will be refined, and these offer great potential to other studies of comparative chromosome mapping. ***