A colored circular muscle, the iris, which is beautifully pigmented giving us our eye's color (the central aperture of the iris is the pupil). This circular muscle controls the size of the pupil so that more or less light, depending on conditions, is allowed to enter the eye. Eye color, or more correctly, iris color is due to variable amounts of eumelanin (brown/black melanins) and pheomelanin (red/yellow melanins) produced by melanocytes. More of the former is in brown eyed people and of the latter in blue and green-eyed people. The Melanocortin-1 Receptor Gene is a regulator of eumelanin production and is located on chromosome(MCIR) 16q24.3. Point mutations in the MCIR gene will affect melanogenesis. The presence of point mutations in the MCIR gene alleles is a common feature in light skinned and blue/green eyed people (J.A.W. Metzelaar-Blok et al., Invest. Ophthal. Vis. Sci. 42,1951-4, 2001; P. Valverde et al. Nat. Genet. 11, 328-330, 1995)).