Some variation in height in humans is due to environmental factors such as diet, exercise and disease. However, if the environmental factors were constant, there would still be continuous variation in height due to such things as bone formation and hormone levels. The more genes that control a characteristic, the more possible gene combinations exist and the more phenotypes. outline the use of highly variable genes for DNA fingerprinting of forensic samples, for paternity testing and for determining the pedigree of animals DNA fingerprinting involves comparing DNA patterns of different fragments from different individuals. Identical patterns of fragment size suggest identical sources of DNA. If enough identical DNA sequences are found, then identification can be determined. Skin, hair or blood cells are frequently used. This is used in forensic science to match blood from suspects at a crime scene, to determine the paternity of a baby, and to determine the pedigree or lineage of individual animals where more than one mating is made. By selecting desirable genes rather than phenotypes, animals and plants can be produced with the preferred characteristics. Examples of these characteristics include disease resistance in certain crops and fish, tolerance of extreme environmental conditions, meat from cattle with low fat.