Improvements through selective breeding have been based essentially on studying the characteristics of plants and animals that are easy to ob serve or measure, their phenotypes. Eye color and body fat are examples of phenotypic traits in animals. Seed size and leaf color are two phenotypic traits found in plants.
Some traits are more important to producers than others.
High protein corn or leaner livestock may earn the producer more money on the market, depending on consumer demand. Other traits like stalk strength or pest resistance make a crop easier to grow and ensure a better yield. Most of these production traits in crops and livestock ultimately depend on the information contained in the DNA of these organisms. Skilled geneticists track such phenotypic features as oil composition in soybeans, fat content in livestock, growth rate in corn, or milk production in dairy cattle to determine individuals whose offspring are likely to be improved for these traits. Techniques to analyze DNA, developed within the last twenty years, are enabling breeders to locate specific DNA genes or chromosome regions that correspond to particular production traits.