Reciprocal recombination (chiasma formation) between homologs appears to be essential for promoting chromosome segregation at the first meiotic division. However, chiasmata that form near the ends of chromosomes are much less efficient at promoting segregation. To determine the frequency of reciprocal recombination near the end of a chromosome, genetic markers were inserted at ~7 kb intervals within the leftmost 30 kb of chromosome I from Saccharomyces cerevisiae. Analysis of recombination between the markers indicated that meiotic reciprocal recombination rates were much lower than on the rest of the chromosome and that rates increased with distance from the telomere. Thus, S. cerevisiae has evolved a mechanism that minimizes the occurrence of chiasmata that cannot promote meiotic segregation. Low rates of recombination were independent of the SIR2 and SIR3 gene products, suggesting that any mechanism for suppressing recombination was different from transcriptional repression due to a telomere position effect.
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