The present invention relates to a method for the production of unsaturated fatty acids with at least two double bonds. The invention furthermore relates to the use of nucleic acid sequences SEQ ID NO: 1, SEQ ID NO: 3, SEQ ID NO: 5 and SEQ ID NO: 11 encoding polypeptides having desaturase activity in the method and for generating a transgenic organism, preferably a transgenic plant or a transgenic microorganism, with an increased content of fatty acids, oils or lipids with unsaturated C18-, C20-, or C22-fatty acids, and to their homologs or derivatives, to gene constructs encompassing these genes, and to their use alone or in combination with biosynthesis genes of polyunsaturated fatty acids. The invention also relates to multiexpression cassettes for seed-specific expression, and to vectors or organisms which encompass a desaturase gene alone or in combination with further desaturases and/or elongase genes or homologs using said expression cassettes.