| Crossover recombination during meiosis permits culling of deleterious mutations from the genome and addition of beneficial sequences, thus facilitating evolution. A priori, the probability of a crossover (CO) at a specific genomic location would equal the probability at any other genomic location. Surprisingly, this is not the case. COs occur preferentially in short intervals called 'hotspots', which are separated by larger 'cold' regions. In many organisms these CO hotspots are also hotspots for double strand breaks (DSBs). Though the mechanism that determines the location of hotspots is not well understood, it is of great interest, as hotspots shape the evolutionary landscape of the genome. Besides their role in evolution, COs also form physical links between homologous chromosomes to facilitate their accurate segregation during meiosis. Without COs, segregation fails, causing aneuploidy and developmental defects. My thesis work shows that CO number and distribution in C. elegans are mediated by a protein complex similar to the chromosome restructuring complex called condensin.;I showed that this new condensin complex is comprised of components from two other condensin complexes in C. elegans, the dosage compensation complex (DCC) and the mitotic condensin complex, both of which preside over chromosome-wide phenomena: X chromosome repression for the DCC, and chromosome compaction and resolution for the mitotic condensin.;Disruption of any component of the hybrid condensin complex increases CO frequency and alters CO distribution. These changes correlate with an increase in DSB frequency and a change in DSB distribution. The alterations in CO distribution and frequency thus appear to be caused by the change in DSBs.;The similarity between this new complex and the mitotic condensin complex suggested that chromosome structure might be altered in these mutants. Assays for chromosome length during DSB formation in meiosis showed a dramatic increase in axis length in the mutants, making it likely that chromosome structure regulates DSB distribution and frequency in wild-type animals. |
