CATLAB (Kinnear 1982), a genetics simulation, was designed to complement conventional genetics instruction. The program enables students to select traits, hypothesize about gene interactions, and decide which cats to cross. The traits students investigate with CATLAB include coat color (white/nonwhite), amount of white spotting (extensive/some/none), density of pigment in the fur (dense/dilute), distribution of pigment in the fur (agouti/nonagouti), tabby striping (mackerel/blotched), and tail or no tail (manx).