Positional cloning identified the melanoma‐inducing Tu locus as a novel receptor tyrosine kinase termed Xmrk (Xiphophorus melanoma receptor tyrosine kinase) [45] that originated from a tandem gene duplication of the Xiphophorus EGFR (epidermal growth factor receptor) gene, and is the fish orthologue of human EGFR. The gene discussed is NTRK1; the disease is melanoma.