Line 304 is a RET transgene that was maintained in a (C57BL/6 x BALB/c)F1 background. The RET transgenic line is a model for melanoma development. A partial congenic line was developed to N3 by crossing (C57BL/6 x BALB/c)F1 transgenic carriers to C57BL/6J. Importantly these N3 congenics were heterozygous for the RET transgene. The N3 RET congenics were crossed to BALB/c and then backcrossed to the N3 RET transgenic line producing 195 backcross mice for the purpose to scan the genome for melanoma phenotypes. Two markers on mouse Chromosome 1 were associated with the early onset of melanoma. The first of these, Melm1 was associated significantly with D1Mit494 (LOD 2.5), with a second marker Melm2 significantly associated with marker D1Mit150 (LOD 4.2). Authors suggest Cxcr4 and Inhbb as candidates for Melm1 and Ifi201, Ifi202a, Ifi203, Ifi204, H25, Itpkb, Tgfb2, Terf1 and Traf5 as candidates for Melm2. Another marker, Melm3 was associated with mouse Chromosome 11.