Chromosomes are the organelles that express, replicate and faithfully transfer the genetic material. We are interested in the mechanism of meiotic chromosome function in the model recombination and then segregate from each other. Meiotic recombination is required for the proper segregation of homologues. However, the mechanisms that control and insure that all chromosomes undergo meiotic recombination are not understood. Chromosome I is the smallest S. cerevisiae chromosome and has a significantly higher rate of meiotic recombination than larger S. cerevisiae chromosomes. The high rate of recombination is necessary to insure that chromosome I homologues always recombine with each other. We will examine the mechanisms that control recombination on this well characterized chromosome. We propose that there is a global control that affects the entire chromosome and may be mediated by crossover interference. Evidence for global control comes from studies that show recombination rates are directly affected by chromosome size. We will characterize this control by studying the effects of moving large regions of chromosome I to larger and smaller chromosomal DNA molecules. We will quantitate the extent of the control and determine whether specific chromosomal sequences are involved. To better understand the mechanism of crossover interference, we will determine the amount of DNA affected by it and isolate mutants that are defective in this control. Finally we will construct a minimal size meiotically functional chromosome fragment that undergoes meiotic recombination at the maximum possible rate. This minichromosome will serve as a model for physical studies on meiotic recombination. The information we obtain in these studies will enable us to better understand how recombination is controlled so that chromosomes pair and segregate properly during meiosis.
