Fatty Acids (FA) from oilseed rape are important nutrition for human diet, renewable sources of energy and raw materials for industry. The oil consists of different types of FA which make the oil more valuable as it can be used for many different purposes. Among these variations, the degree of desaturation plays important role to determine the oil characteristics. Major genes controlling polyunsaturated FA biosynthesis pathway identified in Arabidopsis thaliana have been applied to the oilseed rape breeding, however other genetic regulatory mechanisms are sought after for further manipulation of seed oil composition. Although their effects are quantitative and smaller than those of major genes, they may allow end-users to avoid chemical or physical manipulations which increase cost and other complications. Natural variation in the model plant A. thaliana, a member of the Brassicaceae family, was used in the search for novel loci involved in the regulatory mechanisms of the FA desaturation pathway. Based on the Quantitative Trait Locus (QTL) analysis for the composition of oleic acid, linoleic acid, linolenic acid and seed oil content, Near Isogenic Lines were produced. Subsequently, a QTL for the ratio of FAs linoleic and oleic was chosen for fine mapping with the aid of genomic sequence information from the parental lines. Alongside the fine mapping, comparative mapping is carried out between QTL found in A. thaliana and the pseudo B. napus chromosomes followed by literature search to identify coincident QTL in B. napus. This project is funded by BBSRC, KWS, SAATEN UNION, and MONSANTO.