Fig. 2. Cytotoxic effects of UVBR on melanocytes with different MC1R genotypes. We compared the response to UVBR of NHM 753-c, 830-c and 849-b homozygous or heterozygous for loss-of-function mutations in MC1R to that of NHM 765-c and NHM 755-c, heterozygous or homozygous for Val92Met substitution, respectively. All melanocyte cultures were irradiated a single time with UVBR and cell number and viability were determined on days 2 and 4 after irradiation, as described in Materials and Methods. Each value represents the mean percent cell death of three determinations±s.e.