A polygene, multiple factor, multiple gene inheritance, or quantitative gene is a group of non-allelic genes that together influence a phenotypic trait. Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect. Examples of human polygenic inheritance are height, skin color, eye color and weight. Polygenes exist in other organisms, as well. Drosophila, for instance, display polygeny with traits such as wing morphology, bristle count and many others.