Mutations are changes in the DNA sequence of a cell's genome. When mutations occur, they can either have no effect, alter the product of a gene, or prevent the gene from functioning. Based on studies in the fly Drosophila melanogaster, it has been suggested that if a mutation changes a protein produced by a gene, this will probably be harmful, with about 70% of these mutations having damaging effects, and the remainder being either neutral or weakly beneficial.[68] Mutations can involve large sections of a chromosome becoming duplicated (usually by genetic recombination), which can introduce extra copies of a gene into a genome.[69] Extra copies of genes are a major source of the raw material needed for new genes to evolve.[70] This is important because most new genes evolve within gene families from pre-existing genes that share common ancestors.[71] For example, the human eye uses four genes to make structures that sense light: three for colour vision and one for night vision; all four are descended from a single ancestral gene.[72] New genes can be generated from an ancestral gene when a duplicate copy mutates and acquires a new function. This process is easier once a gene has been duplicated because it increases the redundancy of the system; one gene in the pair can acquire a new function while the other copy continues to perform its original function.[73][74] Other types of mutations can even generate entirely new genes from previously noncoding DNA.[75][76] The generation of new genes can also invo

ve small parts of several genes being duplicated, with these fragments then recombining to form new combinations with new functions.[77][78] When new genes are assembled from shuffling pre-existing parts, domains act as modules with simple independent functions, which can be mixed together to produce new combinations with new and complex functions.[79] For example, polyketide synthases are large enzymes that make antibiotics; they contain up to one hundred independent domains that each catalyze one step in the overall process, like a step in an assembly line. Drosophila melanogaster (Greek for dark-bellied dew lover : ?????? = dew, ????? = lover, ????? = dark-coloured, ?????? = belly[2]) is a species of Diptera, or the order of flies, in the family Drosophilidae. The species is known generally as the common fruit fly or vinegar fly. Starting with Charles W. Woodworth's proposal of the use of this species as a model organism, D. melanogaster continues to be widely used for biological research in studies of genetics, physiology, microbial pathogenesis and life history evolution. It is typically used because it is an animal species that is easy to care for, breeds quickly, and lays many eggs.[3] Flies belonging to the family Tephritidae are also called fruit flies, which can lead to confusion, especially in Australia and South Africa, where the term fruit fly refers to members of the Tephritidae that are economic pests in fruit production, such as Ceratitis capitata, the Mediterranean fruit fly or "Medfly".