The invention relates to processes for the production of unsaturated fatty acids, preferably of conjugated polyunsaturated fatty acids such as conjugated linoleic acid (CLA), by the recombinant expression of desaturases from insects of the order Lepidoptera. Expression preferably takes place in an organism selected from the group of the plant organisms, yeasts, fungi and algae. Also, according to the invention are recombinant expression cassettes for the recombinant expression of desaturases from insects of the order Lepidoptera, and the transgenic organisms transformed with these.