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

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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. ***