One prerequisite for a deeper understanding of genetics of adaptive variation is the identification and analyses of genes affecting such variation. In this thesis, I have searched for genes affecting variation in the adaptive trait flowering time in diffe rent Brassica species. Comparative QTL mapping of flowering time indicated that duplicated copies of one ancestral gene, possibly CONSTANS (CO) might regulate flowering in several Brassica species. A region homologous to the CO region of Arabidopsis thal iana is present in three copies in diploid, and six copies in polyploid Brassica species, and QTL mapped to two out of three regions in the diploids, and three out of six in the polyploid. The two QTL identified in B. nigra were studied further. CO allele s from early and late flowering plants were isolated from both QTL regions (Bni COa and Bni COb). No effect of allelic variation at Bni COa on flowering time was detected when comparing A. thaliana co mutants transformed with the two B.nigra alleles. However, allelic variation at Bni CONSTANS LIKE1 (Bni COL1) located 3kb upstream of Bni COa showed association with flowering time in natural populations of B. nigra. Specifically, an 18 bp indel in Bni COL1 showed significant association with flowering time in several populations. These results and more thorough studies support a hypothesis where a naturally occurring quantitative trait nucleotide (QTN) for flowering time affects the function of Bni COL1 or the expression of Bni COa through variation in the intergenic region between COL1 and COa. Analysis of variation at Bni COb suggested that it has been turned into a pseudogene although some aspects of the data are difficult to reconcile with the loss of function
