Stepping away from anthropocentric models, evolutionary parallels in the wild can provide case studies for understanding what ecological pressures drove the evolution of the first domestication traits. Despite clarification of the timing, locations and genetic processes, most scholars still envision evolutionary responses to human innovations, such as sickle harvesting, tilling, selection for docility or directed breeding. Over the past decade research into early domestication has been transformed by the genomics revolution and increased archaeological investigation. Similar patterns have been observed in homozygous MC1R-deficient mutants in other mammals, implying that the countershading pattern can still be expressed despite the absence of MC1R in the melanocyte. The loss-of-function-mutant rat exhibited a contrasting coat pattern consisting of darker and lighter colors along its dorsal and ventral sides, respectively. This implies that loss-of-function mutations can yield different phenotypes in murine rodents. A spectrophotometer was used to measure coat color, revealing that the rat had a distinctly lighter coat, based on lightness score, than mice with homozygous similar loss-of-function mutations. Upon sequencing the whole coding region of the Mc1r gene (954 bp), we found a 1-bp deletion at site 337 (c.337del), indicative of a frameshift mutation, which was characterized as a severe loss-of-function or null mutation. In this study, we report a case of a wild-caught Norway rat (Rattus norvegicus) from Sado Island, Japan with a yellowish coat color. Changes in MC1R lead to variation in coat color in mammals, which can range from entirely black (melanism) to yellowish. The melanocortin-1 receptor gene (MC1R) controls production of the pigments eumelanin and pheomelanin.
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