Association Genetics can quickly and efficiently delineate regions of the genome that control traits and provide markers to accelerate breeding by marker-assisted selection. The requirements for many markers and a genome sequence to order those markers have limited its exploitation in crops. To harness this approach for use in a broad range of crops, even those with complex genomes, we developed an approach based on transcriptome sequencing to exploit markers representing variation in both gene sequences and gene expression. We term this approach Associative Transcriptomics. Applying it successfully in Brassica napus, as an example, we identified that genomic deletions including orthologues of the transcription factor controlling aliphatic glucosinolate biosynthesis in Arabidopsis thaliana, HAG1 (At5g61420), underlie two QTL for glucosinolate content of seeds.