In mammals and birds, many cases of melanism are caused by amino acid substitutions in the Melanocortin 1 receptor, which controls the shift from pheomelanin to eumelanin production in melanocytes (Majerus and Mundy 2003), although cases in which Melanocortin 1 receptor is not implicated have been reported (Steiner et al. 2009). This evidence concerns the gene MC1R and freckles.