An example of X-linked inheritance

Reciprocal crosses between red-eyed (red) and white-eyed (white) Drosophila give different results. The alleles are X linked, and the inheritance of the X chromosome explains the phenotypic ratios observed, which are different from those of autosomal genes. (In Drosophila and many other experimental systems, a superscript plus sign is used to designate the normal, or wild-type, allele. Here, w⁺ encodes red eyes and w encodes white eyes.)