I remember in high school learning about Punnet squares; people with brown hair had the dominant hair color gene and red hair was recessive. It turns out that it isn’t nearly as simple as having a red hair gene or a brown hair gene. Nor is there a blue eye gene — seems like my teachers were wrong about a lot of things.
So why am I bothering to write about hair color? We all know what our hair color is (or what it was before that box of Clairol ;-). For me, it was not a mystery that I carry the genetic variant for red hair since my dad is a redhead. Now that my son is in college and sporting the beard that every college guy seems to grow, you can see that he carries the variant: his hair is brown but his beard, especially in the sunlight, is surprisingly red. Apparently, the Irish call this a ‘gingerbeard’.
This is important because the genetic variant that causes red shades of hair impacts other aspects of our health as well. Carrying the variant can cause an increased risk of melanoma as well as possibly impact the way you respond to certain analgesics.
Impatient people: jump ahead and check your 23andMe genes for the redhead variant.
Hair color genetics:
There are two types of pigments for hair color: eumelanin and pheomelanin. Eumelanin comes in either black or brown, with varying amounts responsible for ranges of hair color from blond (low eumelanin) to black (high eumelanin). Pheomelanin contributes red and orange coloring. Most people have both eumelanin and pheomelanin, and the varying amounts of each protein contribute to the wide range of hair colors that people naturally have.
The MC1R (melanocortin-1 receptor) gene controls how much melanin vs pheomelanin is produced in the skin and hair. Genetic variants of MC1R produce different amounts of pheomelanin, with increase pheomelanin causing the skin to be more photosensitive along with red hair. The variant forms of MC1R are also thought to not activate DNA repair as well as the more common MC1R form. This leads to higher rates of mutations in the DNA of skin cells, possibly leading to skin cancer. [ref] The link to melanoma is well established for the common MC1R variants that cause red hair, but what people may not realize is that just carrying one copy of the variant doubles the risk of melanoma.[ref]
MC1R isn’t just a human-specific gene; it causes pigmentation variation in animals from chickens to goats to carp. It is also thought to be involved in the browning reaction of cut apples being exposed to air.
Going beyond just the ‘red hair’ gene actually gets really complicated and predicting hair color from genetic data can be tricky. Here is a great article on 124 genes that influence hair color.
Genetic variants of the MC1R gene:
Note that people who are compound heterozygous (e.g. having C/T for rs1805008 and C/T for rs1805007) can also have red hair.
Check your 23andMe results for rs1805008 (v4, v5):
Check your 23andMe results for rs1805007 (v4, v5):
Check your 23andMe results for rs1805006 (v4, v5):
Check your 23andMe results for i3002507 (v4, v5):
Check your 23andMe results for rs2228479 (v4, v5):
If you carry one of the risk variants listed above for melanoma, common sense dictates that you should watch your sun exposure and avoid getting sunburned. While you need a certain amount of sun for vitamin D production, knowing when to cover up or put on sunscreen is important.
So what should you look for in a sunscreen if you are going to use one? The Environmental Working Group has a whole guide to sunscreens and includes research on which ingredients are concerning. High on the list of possibly hazardous ingredients are oxybenzone and octinoxate, both of which penetrate through the skin and have hormone-like activity in the body.