Backcross offspring are from Cross 1. Fish were scored for curve magnitude using a qualitative scale : 0 = non-curved to 4 = extreme curve. Mapping offspring are euthanized at a minimum of 3 months past birth (sexual maturity is at about 1 month past birth), photographed, and frozen in buffered (EDTA) ethanol. The same person scored each individual alive, and then scores were confirmed in photos. Among each phenotypic class (score), the proportion of fish among curved individuals is shown. All fish were photographed on a light table with a digital camera under 3X magnification.