The concept of wild type is useful in some experimental organisms such as fruit flies "Drosophila melanogaster", in which the standard phenotypes for features such as eye color or wing shape are known to be altered by particular mutations that produce distinctive phenotypes, such as "white eyes" or "vestigial wings". Wild-type alleles are indicated with a "+" superscript, for example "w+" and "vg+" for red eyes and full-size wings, respectively. Manipulation of the genes behind these traits led to the current understanding of how organisms form and how traits mutate within a population. Research involving the manipulation of wild-type alleles has application in many fields, including fighting disease and commercial food production.