Abstract

The distribution of meiotic crossover events is not random along chromosomes, but the mechanisms controlling their positioning are as yet poorly understood. Taking a comparative approach between Arabidopsis thaliana and Triticum aestivum, the aim of my project is to establish how crossover frequency across regions rich in disease resistance genes compares to the genome average, and how recombination events contribute to resistance gene supercluster evolution. I characterised a number of T-DNA and Ds insertion lines in A. thaliana to set up a double marker recombinant selection system with view to single nucleotide polymorphism (SNP) assisted mapping of crossover events across resistance gene superclusters on chromosomes 1 and 5. While this project is still work in progress, I can present a crossover frequency map with a fineness of 50kb for the investigated 5Mb region on chromosome 5. I also discovered a number of recombination hotspots, including a 10kb interval of 30cM/Mb containing a tandemly repeated resistance gene, which I am currently characterising further. In addition, I employed a fluorescent pollen reporter line and fluorescence-associated cell sorting to assess if the recombination rate across the resistance gene supercluster on chromosome 5 differs between a range of 20 A. thaliana ecotypes and correlates with the degree of sequence polymorphism. In T. aestivum, I produced and utilised a doubled female haploid population of 1,000 individuals derived from a cross between two divergent varieties (Chinese Spring and Renan) for SNP genotyping to map crossover events across an interval on the best characterised chromosome 3B rich in resistance genes. I can present a preliminary crossover map for this region, which should in the longer term provide insights into the patterns of meiotic recombination of importance for agricultural breeding.