pigmented iris genotype

In the traditional view of eye color, it was taught that two blue-eyed individuals could only produce blue-eyed offspring. For this population a. It was unclear from the outset whether we would have better success considering iris color in terms of four colors (blue, green, hazel, and brown) or in terms of groups of colors. Cassidy, S. B. 2) although some associations were found within nonpigmentation genes such as CYP2C8 at 10q23, CYP2C9 at 10q24, CYP1B1 at 2p21, and MAOA at Xp11.3. .. Chintamaneni C D, Ramsay M, Colman M-A, Fox M F, Pickard R T et al. Many of these strains exhibit biologically and medically relevant phenotypes, including pigment dispersion, a common feature of several human ocular diseases. The P values we obtained for this particular SNP association (P = 0.010.05, depending on the color criteria) were less significant than those described (P = 0.002) by Rebbeck et al. We identified numerous SNPs, haplotypes, and diplotypes (diploid pairs of haplotypes) within the OCA2, MYO5A, TYRP1, AIM, DCT, and TYR genes and the CYP1A2-15q22-ter, CYP1B1-2p21, CYP2C8-10q23, CYP2C9-10q24, and MAOA-Xp11.4 regions as significantly associated with iris colors. Melanin undergoes a packaging process and if large amounts of P protein are not available to process and transport it, the quality of the darker pigment is compromised and lighter shades will result.14 Demonstrating epistasis, the HERC2 gene affects the results produced by the OCA2 gene. Since most individuals of non-European or minority European descent exhibit low variability in iris colors (on average of darker shade than individuals of European descent), this improvement may not seem surprising. At the level of the haplotype, each gene or region had unique numbers and types of associations. Pigment Cell Res 14, 8693 (2001). _____ Pigmented Iris If you are homozygous for the recessive allele "p", you do not produce pigment in the front layer of your iris. Sequences associated with human iris pigmentation. Google Scholar. Article We also acknowledge previous National Science Foundation support under grant numbers 1246120, 1525057, and 1413739. For these subjects, we obtained digital photographs of the right iris, where subjects peered into a box at one end at the camera at the other end to standardize lighting conditions and distance and from which a judge assigned the sample to a color group. The distances between these loci associated with iris colors and neighboring pigmentation genes is far greater than the average extent of LD in the genome, and if it is the case that these associations are through LD, it would seem that, again, population structure would need to be invoked as an explanation. 2000), and adaptin 3B (AP3B) loci (Ooi et al. Eye color ranges include varying shades of brown, hazel, green, blue, gray, and in rare cases, violet and red. The second parent has a non-mutated HERC2 allele but does not have the coding for brown eyes in the OCA2 gene. What is your genotype for this trait? We considered all 61 SNPs in Table 2, their haplotypes in Table 3, and their diplotypes (not shown). Before screening these genotypes for association with iris colors, we used the 73 nonxenobiotic metabolism AIMs to determine BGA admixture proportions for each sample and we tested for correlation between BGA admixture and iris colors. (2002). 2001). Provided by the Springer Nature SharedIt content-sharing initiative, Graefe's Archive for Clinical and Experimental Ophthalmology (2022), Cellular and Molecular Life Sciences (2016), Journal of Human Genetics (J Hum Genet) In other words, the distribution of SNPs among the various genes tested was not random. When a pigment is deposited in the front layer of the iris, this masks the blue layer to varying degrees. Pigmented irises. For some, associations with iris colors were found only within the context of diplotypes, but not at the level of the SNPs or the haplotype (i.e., SILV and GSTT2 genes located at 22q11.23). Montserrat Rabago-Smith. Following your lab manual and your tutor's instructions fill out this table: Trait Phenotype Possible genotypes Class frequency Pigmented iris Pigment No pigment PP Pp pp Pigmented iris = 79% No pigment= 21% Tongue rolling Yes no RR Rr rr 78% can 22% cannot Bent little finger Yes No BB Bb bb 20% can 80% cannot Widow's peak Yes No WW Ww ww . Therefore, it seems that our findings indicate that most of the previous results associating pigmentation gene alleles with iris colors, taken independently, represent merely strokes of a larger, more complex portrait. 2003; T. Frudakis, Z. Gaskin, M. Thomas, V. Ponnuswamy, K. Venkateswarlu, S. Gunjupulli, C. Bonilla, E. Parra and M. Shriver, unpublished observations). Here, we present an analysis of iris phenotypes among 16 mouse strains with mutations influencing melanosomes. Antagonist color refers to the color with which the sequence is negatively associated. A battery of genetic tests, of which one for the inference of iris color could be a part, could enable the construction of a more objective and science-based (partial) physical profile from crime-scene DNA, and an investigator using these tests would be less interested in the biological mechanism of the phenotype than in an ability to make an accurate inference of trait value. Brilliant, M. The mouse p (pink-eyed dilution) and human P genes, ocular albinism type 2 (OCA2), and melanosomal pH. Membrane-associated transporter protein and p protein oculocutaneous albinism II (OCA2) transport melanosomes for melanin maturation. It is inherited or caused by somatic mutations within the cells.2 In addition, it can be caused by the inactivation of particular genes within the cells. OCA2 ranges from 15q11.2-12 and HERC 2 starts at 15q13. To determine the extent to which extant iris color variation could be explained by various models, we calculated R2 values for SNPs, haplotypes, and multilocus genotype data by first assigning the phenotypic value for blue eye color as 1, green eye color as 2, hazel eye color as 3, and brown eye color as 4. 1999; Flanagan et al. . Lighter shades of brown and gray, a lighter shade of blue, show a mixture of two phenotypes where neither dominates completely. The traditional view was correct in which an allele that codes for brown is dominant over green or blue, and green takes precedence over blue.2, Melanocytes in the stroma and anterior layers of the eye hold melanin in their cytoplasms. It is around 12 . Although corrections for multiple testing left most of the SNP-level associations intact, a number of the associations we found did not pass the multiple-testing examination, but nonetheless we present them here to avoid possible type II error; the sequences may be weakly associated with iris colors and possibly relevant within a multiple-gene model for classification (i.e., epistasis). Most of the SNPs within a gene or region were in LD with others in that gene or region (|D| 0.05); only 32 SNP pairsin the MC1R (1 pair), OCA2 (27 pairs), TYR (2 pairs), and TYRP1 (2 pairs) geneswere found to be in linkage equilibrium (not shown). Trace your probable genotype from trait 1 through trait 5 until you . A single SNP in an evolutionary conserved region within intron 86 of the HERC2 gene determines human blue-brown eye Color. One leads to eumelanin, a darker pigment (brown-black), and the other to pheomelanin, a light pigment (red-yellow). A genome scan for eye color in 502 twin families: most variation is due to a QTL on chromosome 15q. Eye color phenotypes demonstrate both epistasis and incomplete dominance. Kayser, M., Liu, F., Janssens, A. C., Rivadeneira, F., Lao, O., van Duijn, K. et al. Although this could indicate that the SNPs are in LD with other phenotypically active loci, it may also be a reflection that variability in message transcription and/or turnover may explain part of the variability observed in human iris colors. Correspondence to Article Second, although a roughly equal number of pigmentation and nonpigmentation gene SNPs were tested, of the 34 marginally associated SNPs, 28 of them. People with blue eyes have no pigment at all in this front layer, causing the fibers to scatter and absorb some of the longer wavelengths of light that come in. The P values we obtained suggested that diplotypes explained more iris color variation than did haplotypes or individual SNPs. (1995) and Koppula et al. .. Kanetsky P, Swoyer J, Panossian S, Holmes R, Guerry D et al. Although research on pigment mutants has made clear that a small subset of genes is largely responsible for catastrophic pigmentation defects in mice and humans, it remains unclear whether or how common single-nucleotide polymorphisms (SNPs) in these genes contribute toward (or are linked to) natural variation in human iris color. The little that isn't absorbed by the iris is reflected back, producing what we see as eye color. Although eye color is usually modeled as a simple, Mendelian trait, further research and observation has indicated that eye color does not follow the classical paths of inheritance. E > e. ee. They help with hormone secretion, which affects the pituitary and can lead to dysfunction of the hypothalamus and other protein complexes. A golden-brown iris indicates the mixture of both eumelanin and pheomelanin (produces the yellow color), and hazel is usually a mixture of brown and green or blue and green, depending on the shade. A brown-iris locus was localized to an interval containing the OCA2 and MYO5A genes (Eiberg and Mohr 1996), and specific polymorphisms in the MC1R gene have been shown to be associated with red hair and blue iris color in relatively isolated populations (Robbins et al. Eye color is determined by the pattern of brown and red pigment, collagen fibers, and the topography of the iris. brown, hazel) P > p. pp. However, a number of the associations we identified were for SNPs located in other types of genes. Heterochromia, although not viewed as a severe disorder, affects many individuals. If you cannot taste anything, you do not possess the dominant allele. Of the 17 that did not, 6 were brown/hazel, 7 were green/hazel, and 4 were blue/green discrepancies although none were gross discrepancies such as brown/green, brown/blue, or hazel/blue. 37.10 Cosmetic iris implant. We also identified associations in the ASIP gene, which supports previous work by Kanetsky et al. This provides an explanation why some babies develop their eye color, but skin pigmentation changes constantly throughout life. Some phenotypes however, are determined by a single gene. However, single-gene studies have not provided a sound basis for understanding the complex genetics of human iris color. Blue eye color in humans may be caused by a perfectly associated founder mutation in a regulatory element located within the HERC2 gene inhibiting OCA2 expression. In all, 27 SNPs were significantly associated with iris pigmentation using at least one of the four criteria, and we refer to these as marginally associated. Sequences of the highest order of complexity within a locus found to be associated with iris colors. Abbott C, Jackson I J, Carritt B, Povey S. Akey J M, Wang H, Xiong M, Wu H, Liu W et al. Nonetheless, the complexity of OCA phenotypes illustrates that TYR is not the only gene involved in iris pigmentation (Lee et al. In humans, eye color is determined by the amount of light that reflects off the iris, a muscular structure that controls how much light enters the eye. The next steps in eye color research involve hue classification among populations. Three genome-wide association studies and a linkage analysis identify HERC2 as a human iris color gene. Jannot, A- S., Meziani, R., Bertrand, G., Gerard, B., Descamps, V., Archibaud, A. et al. Chromosome 15 contains HERC1 and HERC2. In the case of TYR, melanin production will halt entirely, resulting in albinism in the entire body. genotype - all alleles present in the cell ; phenotype - physical appearance of a trait ; . Predicting phenotype from genotype: normal pigmentation. Before the revelation of the effect of HERC2, rs1800407 in exon nine was thought to be the main factor for eye color. They also have little or no coloration in the iris of the eye, giving their eyes a pale blue or pink appearance. Multiple SNPs were identified on chromosome 10q; the CYP2C8-10p23 region had 1 marginally associated SNP, and the neighboring region, CYP2C9-10p24, also had one. Biogeographical ancestry admixture proportions were determined using the methods of Hanis et al. In contrast, between-population comparisons show good concordance; populations with darker average iris color also tend to exhibit darker average skin tones and hair colors. In the rest of the body, the melanin is secreted from the cells. Chromosome 15q harbored the majority (14/27) of the SNPs that were marginally associated with iris colors, and all but one of these 14 were found in two different genes: OCA2 and MYO5A (Table 2). Further, certain of our results support the previous literature. However, the penetrance of each of these alleles appears to be low and, in general, they appear to explain but a very small amount of the overall variation in iris colors within the human population (Spritz 1995). It is toward this goal that we have performed the present study. We sequenced with an ABI3700 using PE Applied Biosystems BDT chemistry and we deposited the sequences into a commercial relational database system (iFINCH, Geospiza, Seattle). When a T is replaced with a C in rs12913832 of intron 86, OCA2 transcription is depressed, resulting in a blue-eyed individual. PubMed However, this result would not have necessarily been obtained were we working with SNPs that were not truly associated with iris colors. To test this, we performed a corrected ANOVA analysis for our data on each of these three levels. Genotyping was performed for individual DNA specimens using a single base primer extension protocol and an SNPstream 25K/ultra-high throughput (UHT) instrument (Beckman Coulter, Fullerton, CA, and Orchid Biosystems, Princeton, NJ). This is an example of a hihybrid crosses. Comparing the results of the two methods of classification, 86 of the classifications matched. Each chromosome contains thousands of individual genes. If you have no pigment you have either blue or gray eyes. Google Scholar. Sturm, R. A., Teasdale, R. D. & Box, N. F. Human pigmentation genes: identification, structure and consequences of polymorphic variation. Nat Genet. There are thought to be about 20,000 genes in human DNA. Within the melanosomes, the tyrosinase (TYR) gene product catalyzes the rate-limiting hydroxylation of tyrosine to 3, 4-dihydroxyphenylanine (DOPA), and the resulting product is oxidized to DOPAquinone to form the precursor for eumelanin synthesis. Complete the table. Redei, G. Encyclopedia of Genetics, Genomics, Proteomics, and Informatics, 3rd edn (Springer, New York City, NY, 2008). Anyone you share the following link with will be able to read this content: Sorry, a shareable link is not currently available for this article. The recessive allele (b) encodes blue eyes. 1997; Box et al. Lastly, disorders involved in eye color include ocular albinism and heterochromia. Most of the marginally associated SNPs were found within the pigmentation genes OCA2 (n = 10), TYRP1 (n = 4), AIM (n = 3), MYO5A (n = 2), and DCT (n =, SNPs marginally (independently) associated with iris pigmentation and SNPs associated only within the context of haplotypes and/or diplotypes. The mouse pink-eyed dilution gene: association with human Prader-Willi and Angelman Syndromes. This gene is often referred to as the red-headed gene because of its prevalent expression in people with red hair and green eyes.4 Dopachrome tautomerase also contains regions for hazel and green eyes.5 Regions for brown eyes dominate the effects of these genes, though. An individual with this disorder produces little or no pigment in their ocular melanocytes. Department of Chemistry and Biochemistry, Kettering University, Flint, MI, USA, You can also search for this author in This also explains why deletions within HERC2 would cause a decrease in melanin without interacting with the P protein itself. Liu, F., Wollstein, A., Hysi, P. G., Ankra-Badu, G. A., Spector, T. D., Park, D. et al. This condition is pronounced in people who produce little to no pigment throughout their entire body, but it can be localized to the eyes.2 When they produce no pigment at all, it is usually due to a nonfunctioning TYR.10 With this condition, a complete lack of pigment produces red eyes, and a small amount of pigment may produce violet eyes. When light passes through a large amount of melanin, most of the visible light is absorbed, and the little that is reflected back appears brown. Many more genes affect brown and blue more than the other eye colors. Green eyes require more pigment than blue and not much less than brown, and because the shades of hazel (brown with blue or green) are more versatile, hazel is still more popular than green. We have applied a nonsystematic, hypothesis-driven genome-screening approach to identify various SNPs, haplotypes, and diplotypes marginally (i.e., independently) associated with iris color variation. The colored area at the front of the eye is called the iris. European J Hum Genet 13, 913920 (2005). The process that produces melanin, known as melanogenesis, requires numerous proteins. To form eumelanin, dopachrome tautomerase, TYR, and TYR-related protein 1 complete the chemical pathway from dopaquinone.3, Although the aforementioned proteins are responsible for the production of melanin, once it has been produced in the melanosomes, other proteins are responsible for melanin maturation. Hum Mutat 13, 99115 (1999). PubMedGoogle Scholar. The large HERC2 gene requires 211kb and 93 exons that codes for a 528kDa protein made of 4834 residues.12. Google Scholar. Tyrosinase (TYR), the enzyme responsible for pigment production in the body, starts the synthesis of both types of melanin by catalyzing a reaction between tyrosine and dopa, forming dopaquinone. and JavaScript. These two seemingly unrelated genes have a major effect on eye color in humans. Phakomatoses. In Drosophila, iris pigmentation defects have been ascribed to mutations in >85 loci contributing to a variety of cellular processes in melanocytes (Ooi et al. HERC2, a large ubiquitin ligase, contains the promoter region for OCA2, the P protein. The pedigree in the accompanying illustration shows the inheritance of albinism, a homozygous recessive condition resulting in a total lack of pigment. This finding, while common with albinism, is not specific as iris transillumination occurs in diseases unrelated to albinism such as pseudoexfoliation, pigment dispersion syndrome . Now, that color depends on the kind and density of melanin a person is born with. In the most elementary form, the inheritance of eye color is classified as a Mendelian trait.1 On the basis of the observation of more than two phenotypes, eye color has a more complex pattern of inheritance. Am J Hum Genet 82, 424431 (2008). The most strongly associated of the marginally associated SNPs were from the OCA2, TYRP1, and AIM genes, in order of the strength of association, which is the same order as that provided using the number of marginally associated SNPs, rather than their strength. 1993; Valverde et al. Transcribed image text: P>p Trait Genotype Phenotypic Effect Relationship P. Pigmented Iris (Additional genes give specific Iris Color color, e.g. MGG 1, 393394 (1908). 5.01 In an experiment designed to study the inheritance of flower color in four-o'clocks, two plants with pink flowers were crossed. If no haplotypes were found to be associated for a locus but diplotypes were found to be associated, both the haplotypes and the diplotypes are shown. Zhu, G., Evans, D., Duffy, D., Montgomery, G., Medland, S., Gillespie, N. A. et al. 1998), but mouse studies have suggested that 14 genes preferentially affect pigmentation in vertebrates (reviewed in Sturm et al. Article The OCA2 gene also contains numerous regions for eye color expression. record your observations. ), Molecular analysis of type I-A (tyrosine negative) oculocutaneous albinism, Molecular basis of type I (tyrosinase-related) oculocutaneous albinism: mutations and polymorphisms of the human tyrosinase gene, Molecular basis of albinism: mutations and polymorphisms of pigmentation genes associated with albinism, Altered expression of a novel adaptin leads to defective pigment granule biogenesis in the Drosophila iris color mutant garnet, P gene as an inherited biomarker of human eye color, Pigmentation phenotypes of variant extension locus alleles result from point mutations that alter MSH receptor function, Loss of function mutations of the human melanocortin 1 receptor are common and are associated with red hair, Molecular basis of dark-eyed albinism in the mouse, Skin pigmentation, biogeographical ancestry and admixture mapping, Melanocortin 1 receptor variants in an Irish population, Empirical Bayes adjustments for multiple results in hypothesis-generating or surveillance studies, A new statistical method for haplotype reconstruction from population data, Molecular analysis of two mouse dilute locus deletion mutations: spontaneous dilute lethal-20J and radiation-induced dilute prenatal lethal Aa2 alleles, Human pigmentation genes: identification, structure and consequences of polymorphic variation, Variants of the melanocyte-stimulating hormone receptor gene are associated with red hair and fair skin in humans, A mutation in Rab27a causes the vesicle transport defects observed in ashen mice, Exact tests for association between alleles at arbitrary numbers of loci, This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (, Selection and Geography Shape Male Reproductive Tract Transcriptomes in Drosophila Melanogaster, From Multi-Allele Fish to Non-Standard Environments, How ZFIN Assigns Phenotypes, Human Disease Models, and Gene Expression Annotations to Genes, Genetic association models are robust to common population kinship estimation biases, 101 years ago: Hermann Muller's remarkable insight, https://doi.org/10.1093/genetics/165.4.2071, https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model, Receive exclusive offers and updates from Oxford Academic, Adaptor-related protein complex 3, -1 subunit, Adaptor-related protein complex 3, -1 subunit, Copyright 2023 Genetics Society of America. Phenotypic Effect. No significant SNP associations within the pigmentation genes SILV, MC1R, ASIP, POMC, RAB, or TYR were found, although TYR had one SNP with a P = 0.06. To obtain Although TYR is centrally important for this process, pigmentation in animals is not simply a Mendelian function of TYR or of any other single protein product or gene sequence. The decreased expression could account for incomplete dominance, as well. As the eye color lightens, less melanin is present in the cells, reflecting more of the visible spectrum. Genetics 165, 20712083 (2003). OCA2 contains regions for the numerous eye colors, but one SNP is a strong predictor for brown/blue eyes. bb genotype for the phenotype of blue eyes. Diplotypes for these 61 alleles explained most of the iris color variance in our sample; the lowest amount was explained at the level of the SNP, suggesting an element of intragenic complexity to iris color determination (i.e., dominance). Question: In albinism (a recessive disorder), the formation of melanin, a dark skin pigment, are blocked so that albinos have extremely light skin and hair. It is interesting that most of the SNPs that we discovered are noncoding, either silent polymorphisms or SNPs residing in the gene proximal promoter, intron, or 3 UTR, which is not altogether unusual. In fact, study of the transmission genetics for pigmentation traits in humans and various model systems suggests that variable pigmentation is a function of multiple heritable factors whose interactions appear to be quite complex (Brauer and Chopra 1978; Bito et al. (2002), although it should be noted that we did not observe this gene association at the level of the SNP as they did; one of the ASIP SNPs that we identified (marker 861, Table 2) is the 8818 G-A SNP transversion that they described to be associated with brown iris colors, but from our study the association was with hazel color at the level of the haplotype. Although cysteine is not an essential amino acid and its deficiency rarely occurs, the lack of it halts the production of pheomelanin. . Others genes such as AIM, OCA2, and TYRP1 harbored haplotypes positively associated with brown but negatively associated with blue color (AIM haplotype 2; OCA2 haplotypes 2, 4, 45, 47; TYRP1 haplotype 4; Table 3) while others, such as the MYO5A, OCA2, TYRP1, and CYP2C8 genes located at 10q23, harbored haplotypes positively associated with one color but not negatively associated with any other color (MYO5A haplotype 5 and haplotype 10, OCA2 haplotype 19, TYRP1 haplotype 3, and CYP2C8 haplotype 1; Table 3). This page titled 8.2: Human Traits Determined by Single Genes is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Ellen Genovesi, Laura Blinderman, & Patrick Natale via source content that was edited to the style and standards of the LibreTexts platform; a detailed edit history is available upon request. Eiberg, H., Troelsen, J., Nielsen, M., Mikkelsen, A., Mengel-From, J., Kjaer, K. et al. Thank you for visiting nature.com. Other genes determine the nature and density of the pigment, giving us brown, hazel, violet, green and other eye colors. 1996), melanocortin receptor (MC1R; Robbins et al. .. Rebbeck T R, Kanetsky P A, Walker A H, Holmes R, Halpern A C et al. In terms of disease, OCA2 and MC1R were linked to melanoma. .. Bito L Z, Matheny A, Cruickshanks K J, Nondahl D M, Carino O B. Boissy R E, Zhao H, Oetting W S, Austin L M, Wildenberg S C et al. Half of the associated SNPs were located on chromosome 15, which corresponds with results that others have previously obtained from linkage analysis. Nature 361, 7276 (1993). We identified 5 additional genes (ASIP, MC1R, POMC, and SILV) and one additional region (GSTT2-22q11.23) with haplotype and/or diplotypes, but not individual SNP alleles associated with iris colors. We thank D. C. Rao, Director of the Division of Biostatistics, Washington University, St. Louis, for help preparing this manuscript; Mark Shriver, Department of Anthropology and Human Genetics at The Pennsylvania State University for his help with the biogeographical ancestry admixture aspect of the project; and Murray Brilliant, professor of Pediatrics and Molecular and Cellular Biology at the University of Arizona for their kind advice and support of our work. .. Copeland N G, Hutchison K W, Jenkins N A. Durham-Pierre D, Gardner J M, Nakatsu Y, King R A, Francke U et al. The gene contains a main coding region for brown eyes (BEY2 15q11-15) and hazel eyes (BEY1).3, 5 Other SNPs result in blue and green eyes. Use two alleles per trait for the genotype. In this case, pleiotropic effects change eye color. Producing multicolored irises, heterochromia stems from mutations in certain cells of the iris. volume56,pages 57 (2011)Cite this article. Specify the following genotypes using A and a to indicate dominant and recessive alleles, respectively. For full access to this pdf, sign in to an existing account, or purchase an annual subscription. Legal. We also thank Robert White for his help with sample collection. Hurst, C. C. On the inheritance of eye colour in man. PubMed .. Steenland K, Bray I, Greenland S, Boffetta P. Strobel M C, Seperack P K, Copeland N G, Jenkins N A. Valverde P, Healy E, Jackson I, Rees J L, Thody A J. Wilson S M, Yip R, Swing D A, OSullivan T N, Zhang Y et al. (82%) were in pigmentation genes. Decreased expression of OCA2 affects the pathway for melanosome maturation. lack pigment in skin (recessive) pigmented iris - pigments (dominant) hides blue/gray color of iris back layer ; attached earlobes - free earlobes dominant over attached earlobes ; hitchhiker's thumb - last joint of thumb bends back over 60 degrees . IRIS pigmentation is a complex genetic trait that has long interested geneticists, anthropologists, and the public at large. Pathway I contains gene A that produces an enzyme to catalyze conversion of a colorless pigment designated white1 to blue pigment. At the cellular level, variable iris color in healthy humans is the result of the differential deposition of melanin pigment granules within a fixed number of stromal melanocytes in the iris (Imesch et al. Specimens for genotyping were of self-reported European descent, of different age, sex, hair, iris, and skin shades and they were collected using informed consent guidelines under Investigational Review Board guidance. trends Genet. A three-single-nucleotide polymorphism haplotype in intron 1 of OCA2 explains most human eye-color variation. Although there are about 16 different genes responsible for eye color, it is mostly attributed to two adjacent genes on chromosome 15, hect domain and RCC1-like domain-containing protein 2 (HERC2) and ocular albinism (that is, oculocutaneous albinism II (OCA2)).

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