Gamete genetic diversity is increased via meiotic crossover between homologous chromosomes. Heterozygous polymorphisms are known to influence recombination patterns through both cis and trans modification. We have crossed fluorescent crossover reporters to a global panel of Arabidopsis accessions and tested for crossover modification by polymorphism. We observe substantial variation in euchromatic and centromeric recombination rates between F1 heterozygotes. In many cases F1 crossover frequency is higher than in homozygotes, ruling out that recombination is simply suppressed by polymorphism. We also observe dramatic variation in recombination rates between F2 recombinants in the next generation. In this project the student will further analyse high recombination F2 populations and map the segregation of cis and trans modifiers of crossover rate. They will use high-throughput fluorescent assays that allow us to score 1,000s gametes per plant using flow cytometry (See Yelina et al., (2013) Nat. Protocols 8: 2119-34). Mapping and sequencing will be used to identify recombination modifiers, which will then be studied mechanistically. The results of this work will have direct relevance to crop breeding, which relies on meiotic recombination. The student's findings will also have evolutionary significance, as recombination modifiers are speculated to exert a strong effect on selection of genetic variation in natural populations.