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As of 2010, as many as 16 genes have been associated with eye color inheritance. Some of the eye-color genes include OCA2 and HERC2. [9] [10] The earlier belief that blue eye color is a recessive trait has been shown to be incorrect, and the genetics of eye color are so complex that almost any parent-child combination of eye colors can occur.
For example, having eye color is a character of an organism, while blue, brown and hazel versions of eye color are traits. The term trait is generally used in genetics , often to describe phenotypic expression of different combinations of alleles in different individual organisms within a single population , such as the famous purple vs. white ...
A null allele is a gene variant that lacks the gene's normal function because it either is not expressed, or the expressed protein is inactive. For example, at the gene locus for the ABO blood type carbohydrate antigens in humans, [13] classical genetics recognizes three alleles, I A, I B, and i, which determine compatibility of blood transfusions.
Color blindness may also present itself as a symptom of degenerative diseases of the eye, such as cataract and age-related macular degeneration, and as part of the retinal damage caused by diabetes. Vitamin A deficiency may also cause color blindness. [47] Color blindness may be a side effect of prescription drug use.
The ancestral allele is linked to darker pigmentation and dominant over the lighter pigment recessive allele. [10] [11] The rs12913832 SNP, located in intron 86 of the HERC2 gene contains a silencing sequence that can inhibit the expression of OCA2 and, if both recessive alleles are present, can homozygously cause blue eyes. [12]
The reason boils down to genes. A senior lecturer in biomolecular sciences at Liverpool John Moores University said, "What we know now is that eye color is based on 12 to 13 individual variations ...
A single copy of the allele has minimal impact on eye color, but when two copies are present, a horse will be blue-eyed in addition to a light coat color. The cream gene is one of several hypomelanism or dilution genes identified in horses. Therefore, it is not always possible to tell by color alone whether the C Cr allele is present without a ...
Some genetic traits are instantly visible, such as eye color or the number of limbs, others are not, such as blood type, the risk for specific diseases, or the thousands of basic biochemical processes that constitute life. A gene can acquire mutations in its sequence, leading to different variants, known as alleles, in the population.