Centromeres are the chromosomal loci where microtubule spindles bind, via the kinetochore, during mitosis and meiosis. Paradoxically the centromere, as a functional unit, is essential to guarantee faithful chromosome segregation, whereas its underlying DNA sequences and associated kinetochore proteins are fast evolving. In most animals and plants that have been studied, centromeres contain megabase-scale arrays of tandem repeats. In spite of their importance, very little is known about the degree to which centromeric tandem repeats share common properties between different species across different phyla. We used bioinformatic methods to identify high-copy tandem repeats from species using publicly available genomic sequence and our own data. We found that despite an overall lack of sequence conservation, centromeric tandem repeats from diverse species showed similar modes of evolution. Furthermore, phylogenetic analysis of sequence homology showed little evidence of sequence conservation beyond approximately 50 million years of divergence. In addition, we performed a survey of fungi genomes for the presence of high-copy tandem repeats, but found little evidence to suggest that high-copy centromeric repeats are a common feature feature in fungi, with the possible exception of the Zygomycota. phylum. Finally, in most species the kinetochore assembles at a single locus, but in some cases the kinetochore forms along the entire length of the chromosomes forming holocentric chromosomes. Following a literature review we estimate that holocentricity is very common and has evolved at least thirteen times.
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|Advisor:||Korf, Ian F., Chan, Simon WL|
|Commitee:||Dawson, Scott C., Langley, Charles H.|
|School:||University of California, Davis|
|Department:||Cell and Developmental Biology|
|School Location:||United States -- California|
|Source:||DAI-B 75/03(E), Dissertation Abstracts International|
|Subjects:||Genetics, Evolution and Development, Bioinformatics|
|Keywords:||Centromere, Chromosomes, Eukaryotes, Evolution, Holocentric, Tandem repeat|
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