Polyploidy is very common among plants but having multiple sets of chromosomes creates additional challenges for chromosome pairing and recombination during meiosis. Brassica napus is an allotetraploid comprised of the A and C genomes from B. rapa and B. oleracea, respectively. In adapted B. napus lines, the chromosomes of the A and C genomes pair almost exclusively with their true homologue during meiosis, but in newly resynthesized B. napus plants there is a significant increase in pairing between homoeologues, the closely related chromosomes from the other genome, i.e. A/C pairings. This interaction between homoeologues can result in an uneven distribution of chromosomes in the gametes so restricting pairing is important for overall plant fitness. However, this unequal crossing over can also serve to introduce novel variation allowing for species diversification and adaptation.
I have developed a new method for detecting homoeologous recombination events in B. napus using a single nucleotide polymorphism (SNP) array. Traditionally scientists have used cytology or restriction fragment length polymorphism markers but the SNP array offers much quicker data generation and a higher density of markers for more precise identification of crossover points and detection of smaller exchanges. Using this new methodology I measured recombination between the A and C genomes in natural B. napus lines and have shown that homoeologous exchanges continue to happen in modern B. napus cultivars at a relatively high frequency.
I have also used the SNP array to analyze a resynthesized B. napus population segregating for the level of homoeologous recombination and mapped three quantitative trait loci (QTL) controlling this phenomenon. Further analysis of the genes underlying these QTL can help to identify the mechanisms that have evolved in natural B. napus to control meiotic chromosome pairing and manipulation of those genes could be used to increase homoeologous recombination rates to introduce novel traits from diverse species
