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OverviewEdit

Hair color is dependent on only two pigments or types of melanin; brown-black eumelanin and red-yellow pheomelanin.  While brown-black eumelanin is predominant in those with brown and black hair, red-yellow pheomelanin predominates in those with red hair.  

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Blonde hair appears so lightly because it is a result of low amounts of both pigments.  In contrast, large amounts of both produce darker or black hair.  The predominant hair color in this world is black.  Colors such as red, blonde, and brown are actually shown to only result from European ancestry (1 ).

SNPs and Hair ColorEdit

There are currently only two known single nucleotide polymorphisms (SNPs) correlating with hair color.  SNP rs1805007, in the MC1R gene, encodes a protein used in melanin production.  Each T nucleotide at this single nucleotide polymorphism increases the odds of having red hair by 6.1 times. 

Hair-melanin

Courtesy of NIH Medical Encyclopedia (4).

The MC1R gene codes for a protein called the melanocortin I receptor, which essentially controls the type of melanin produced by melanocytes, being either eumelanin or pheomelanin.  If the receptor is activated, a chemical cascade is triggered inside the melanocytes that stimulate eumelanin production.  If the receptor is either inactivated or blocked, the melanocytes produce pheomelanin instead (2 ).  SNP rs1667394, in the OCA2 gene, also plays a role in pigmentation.  Each C nucleotide in this single nucleotide polymorphism decreases the odds of having blonde vs. brown hair by 5 times (1 ).  The OCA2 gene, or the oculocutaneous albinism II gene, encodes P protein which is also located in melanocytes.  Although the precise function of P protein is unknown, it is found to be important in the determination of skin, eye, and hair color, most likely involved in melanin production as well (3 ).

Genotype ResultsEdit

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John Burke carries genotype CT for single nucleotide polymorphism rs1805007, making him at “substantially higher odds of having red hair.”  This means he is within 2.5 - 9.9 times at risk (1 ).  His T nucleotide is what makes him more likely to have red hair.

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Dr. Burke also carries genotype TT for single nucleotide polymorphism rs1667394, meaning he is at “typical odds of having blonde hair vs. brown hair (1 ).”  His TT nucleotide base pair is what makes him most likely to be blonde over brunette.

Both of these single nucleotide polymorphisms are only applicable to European ethnicity, meaning Dr. Burke is from fairly strong European decent. 

References

1. Sulem P et al. (2007). “Genetic determinants of hair, eye and skin pigmentation in Europeans.” Nat Genet 39(12):1443-52.

2. Genetics Home Reference. MC1R. National Institute of Health, 2014. Web.

3. OCA2. Wikipedia, 2014. Web.

4. Medline Plus Medical Encyclopedia. National Institute of Health, 2014. Web.