Hair Curl: How it Works
As you all know, I had my DNA tested by 23andme. I learned so many interesting things about my DNA and human science in general. Although this information is not available through 23andme anymore, I was fortunate to have access to some of their health information.
I found this portion interesting since I am all about Natural hair!
My Result: "Genotype GG: Slightly curlier hair on average.
Genes Vs. Environment:
Hair texture is highly heritable, with heritability estimates ranging between 85-95%. High heritability means that the trait is controlled almost entirely by your genes—environmental factors play little or no role. Which genes and variations control hair texture, however, are not well understood. The SNP reported here by 23andMe accounts for less than 10% of the variation in hair curl seen in European populations.
From stick straight to wavy to twisty to kinky—the texture of human hair runs the gamut. Hair's curliness (or lack thereof) comes from the shape of the bulb at the base of the hair follicle. In people of all ethnicities, a curved bulb translates into curly locks. Not surprisingly, this biological trait has a strong genetic component, although a simply inherited "hair curl" gene that completely determines hair texture has not been found and likely does not exist. Instead, variations in several genes affecting different aspects of hair development probably combine together to determine the shape of your 'do.
From stick straight to wavy to twisty to kinky—the texture of human hair runs the gamut.
For much of the history of hair research, hair has been categorized based on ethnic differences. Hair from people with African ancestry tends to be intensely kinked. People with Asian ancestry tend to have coarse, thick hairs that hang straight. Europeans are more varied. About 45% have straight hair, 40% have waves, and 15% have curly hair.
As the science has progressed, researchers have moved away from descriptions based on ethnicity, and focused instead on the molecular details of different hair types.
The Root Cause
When straight and curly hairs are examined closely, it's clear that there are differences in the distribution of certain cells and proteins. In curly hair, the important hair components are distributed more asymmetrically than they are in straight hairs.
The root (pun intended) of the asymmetry found in curly hairs has been shown to be the golf club-shaped bulb at the base of the hair follicle. As a hair grows out from such a curved bulb, cells on the outside and inside of the curve develop at different rates and filaments of keratin are deposited in differing arrangements.
Curved hair bulbs have the same effects in people of all ethnicities. In fact, the shape of the bulb is so central to hair curl that follicles removed from the head and grown in a lab dish continue to produce straight or curly hairs.
Learn More About TCHH
Whether your hair is curly or straight, it's probably a lot like the hair you see all around you in your family. That's because genetics play a large part in determining hair texture. No single "hair curl" gene has been discovered, however.
Studies (including 23andWe research that used survey answers provided by 23andMe customers) have shown that variation near the TCHH gene determines a small part of hair curl in Europeans. On a scale of 0 to 5 (0 being straight, 5 being super curly), each copy of the A version of rs17646946 was associated with a reduction of about 0.29 curliness points.
The TCHH gene encodes a protein called trichohyalin, which is known to be expressed at high levels in hair follicles and has been shown to be involved in cross-linking of the keratin filaments found in hair in skin.
23andMe researchers have also identified another SNP associated with hair curl. This association, however, has not yet been replicated by other scientists. Read more in the Hair Curl Preliminary Research Report. You can also learn about a genetic variation found mainly in people with Asian ancestry that has been associated with hair thickness in the Hair Thickness Preliminary Research Report."
"The genotyping services of 23andMe are performed in LabCorp's CLIA-certified laboratory. The tests have not been cleared or approved by the FDA but have been analytically validated according to CLIA standards. The information on this page is intended for research and educational purposes only, and is not for diagnostic use."
If you are interested in starting your own DNA journey,
click here--> 23andme
Also, make sure to follow me on Instagram to learn about my Genealogy results (on 3/14/14)