You can probably do what you want with this content see the permissions page for details.Ang M, Wong W, Park J, et al. Sparky House Publishing, Baltimore, Maryland. This page was last revised December 8, 2011. Pigment Cells and Melanoma Research 22: 544-562. Genetics of human iris colour and patterns. Gene-gene interactions contribute to eye colour variation in humans. Changes in eye color during early childhood: sex and genetic differences. Clinical and Experimental Ophthalmology 39: 462-471. Classification of iris colour: review and refinement of a classification schema. Digital quantification of human eye color highlights genetic association of three new loci. Proceedings of the Royal Society of London B 80: 85-96. The heredity of eye color and hair color in man. American Journal of Physical Anthropology 43: 387-391.ĭavenport, G. American Journal of Physical Anthropology 2: 15-20.īrues, A. Archives of Ophthalmology 115: 659-663.īoas, H. Eye color changes past early childhood: the Louisville Twin Study. Instead, eye color is determined by variation at several different genes and the interactions between them, and this makes it possible for two blue-eyed parents to have brown-eyed children. 2011).Įye color is not an example of a simple genetic trait, and blue eyes are not determined by a recessive allele at one gene. However, variation in at least 10 other genes, plus complicated interactions between these genes, also influences eye color (reviewed in Sturm and Larsson 2009, with more recent results in Liu et al. Molecular geneticsĪ number of groups surveyed associations of single-nucleotide polymorphisms with eye color, with fairly consistent results: variation in the HERC2 and OCA2 genes, which are next to each other on chromosome 15, plays a major role in determining eye color. Surprisingly, there don't seem to have been any parent-offspring studies of eye color since then, at least none that I could find. Boas (1918) found an even larger number of non-blue-eyed offspring of two blue-eyed parents, 26 out of 223. Out of 52 offspring of two blue-eyed parents in their data, one had brown eyes and two had gray eyes, which does not fit the idea that blue eyes are caused by a recessive allele. Holmes and Loomis (1909) criticized the earlier work, saying that eye color varies continuously, and dividing it into categories is arbitrary. He found the following results: Parentsīecause there are no "duplex" (non-blue-eyed) offspring of two blue-eyed parents, these data fit the model of blue eyes being caused by a recessive allele at one gene. Hurst (1908) divided eyes into just two types, "simplex" (blues and some grays, with no pigment on the outer surface of the iris) and "duplex" (all other colors). The authors said "we suspect to be of a blue type," whatever that means. They claimed that whenever both parents had blue eyes, all of the children have blue eyes, but their data actually included two hazel-eyed offspring of blue-eyed parents. Family studiesĭavenport and Davenport (1907) were the first to suggest that blue eye color was caused by a recessive allele. Some people have a blue or green iris with a brown ring around the pupil (Sturm and Larsson 2009), which makes the classification of eye color even more complicated. Eye color can change dramatically in the first few years of life, as many babies are born with blue eyes but then develop green or brown eyes (Matheny and Dolan 1975), and changes can also occur later in life (Bito et al. 2011) or the hue and saturation values quantified (Liu et al. This has been criticized as an oversimplification (Brues 1975), and eye colors have been divided into nine categories (Mackey et al. Many studies divide eye colors into three categories: blue (or blue and gray) green and hazel and brown. Blue, gray, green and hazel eyes are only common in people of European ancestry other people's eyes are various shades of brown. Irises with little melanin appear blue due to scattering of light by collagen fibers in the iris. The color of the iris is determined by the amount of melanin, the ratio of eumelanin (which is dark brown) to pheomelanin (which is reddish), and the way the melanin is distributed in the eye. Many people who know nothing else about genetics think that two blue-eyed parents cannot have a brown-eyed child. One of the oldest myths in human genetics is that having blue eyes is determined by a single gene, with the allele for blue eyes recessive to the allele for non-blue eyes (green, brown, or hazel).
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