Abnormal individuals with anatomical changes consisting largely of overgrowth or undergrowth of wings, bristles, eye grid, and reproductive organs appear sporadically and in ratios to the normal varying from 1 in 25 to 1 in 100 in a special stock of D. melanogaster. Fertility is reduced and life shortened in affected individuals. These variations are associated with a change of chromosome numbers, there usually being 12 instead of the usual 8. A 3rd chromosome recessive gene brings about these chromosome changes at maturation division.