Provided are nucleic acid sequences from Brassica oleracea plants that encode enzymes involved in the synthesis of a glucosinolate molecule, including BoGSL-ALK, and BoGSL-ELONG, and methods of their use. The sequences find particular use in modifying the glucosinolate content of a plant. Also provided are primers for these two genes and a third key gene in the glucosinolate pathway, BoGSL-PRO, that can be used for developing molecular markers for assisted selection of plants with specific glucosinolate compositions. Additionally, compositions and methods for a simple, reliable and efficient PCR-based marker system, named sequence-related amplification polymorphism (SRAP), that finds use in the identification of coding sequences in the genome of a plant are provided.