Available at: http://digitalcommons.calpoly.edu/theses/1126
Date of Award
MS in Biological Sciences
Allopolyploids form through the hybridization of two or more diploid genomes. A challenge to reproduction in allopolyploids is that pairing can occur between homologous chromosomes or homeologous chromosomes (i.e.different subgenomes.). Crossover between homeologous chromosomes can result in chromosome rearrangements that lower fertility and overall fitness. Rearrangements can alter the dosage of either entire chromosomes or just parts of chromosomes. Understanding the frequency and extent of rearrangements will help to explain the evolution and genome stabilization of agriculturally important allopolyploid species. Pyrosequencing is a useful tool in the study dosage changes in allopolyploids because it allows quantification of the relative contribution from each progenitor species at any given locus. Here we use pyrosequencing to analyze resynthesized Brassica napus allopolyploids and their progeny. Targets for pyrosequencing were identified using a bioinformatic approach taking advantage of recently-released Brassica genome sequence. SNPs identified through bioinformatics were confirmed through molecular biology. Markers along the A3/C3 homeolog pair were used to identify the occurrence of novel homeologous exchanges during meiosis in the parent plant, and segregation patterns arising from dosage changes in the parent. We identify a higher frequency of homeologous rearrangements at the distal end of the chromosomes. We also observe that the presence of a dosage change in a parent increases the likelihood that the chromosome bearing the dosage change will undergo subsequent rearrangements in neighboring loci.