Nearly all sexually reproducing organisms make gametes via the complex cell divisions known as meiosis. At an early stage of meiosis I, the two homologous chromosomes pair with each other, first at specific (but poorly understood) chromosome regions and then along the entire length of the chromosome. A critical aspect of this process is crossing over, in which the two homologues exchange genetic material. Crossing over results in genetic combinations not found in either parent. Perhaps more significant, the physical connection provided by crossing over holds the homologues together during meiosis I and allows the orderly separation of homologues at the end of meiosis I.
Both the number and the location of crossovers is regulated, but the process by which this control is exerted is unknown. Chromosomes at the beginning of meiosis become much thicker and shorter, so one possibility is that crossover control is part of chromosome compaction. Direct evidence for this hypothesis is lacking.
Philip Meneely and students working with him study crossover control in the nematode worm Caenorhabditis elegans. C. elegans is a very well-studied animal - the first multicellular organism to have its genome completely sequenced - and genes that affect the number and location of crossovers have been found. Our expectation is that by understanding these genes we will begin to understand the molecular mechanism of crossover control.