Theme: Sex Differences

WHY DO SO MANY ASHKENAZIM HAVE RED HAIR?
(not complicated – sorta….)

1) Back haired south eurasian semititic male jews from the levant.
2) Brown, Blonde, Red, haired European Women from the Roman Region
3) Immediate inbreeding.
4) Jewish population bottlnecks
5) Continued Extraordinary inbreeding creating extraordinary mutations – ie: why jews are more vunlerable to genetic defects and diseases.
6) Coloring, especially hair, is polygenic. Though one gene in particular carries heavy influence.
7) Small groups with similar complex mutational load combined with polygenic expression, selected for memory, verbal and calculation skills, selects for female traits, yielding european coloring bias. (Yes, turns out that historical observation as well as present suspicions are true. 😉 )

Summary,
European female introgression, european female bias in recursive trait selection, inbreeding, mutation, bottlenecking. (Kinda neat really.)

Sidebar:
(One of my best friends is a prototypical tall, large round- headed, blue eyed, red haired half jewish male working in the upper reaches of the financial sector. My wife had long red hair. So did my best friend when I was younger. So did my first girlfriend. While my hair was originally blond and matured into taupe (mouse brown), and now as I’m older it’s darker brown, I had quite abit of red and blonde in my beard before it went grey. So I’m kind of partial to red hair. (Very))

GENETICS OF THE COLOR OF HAIR
The coloration of hair is primarily determined by the type, amount, and distribution of pigments called eumelanin and pheomelanin, produced by cells known as melanocytes. These pigments are influenced by a variety of genes and single-nucleotide polymorphisms (SNPs). Here are some primary genetic distinctions:

Note: (a) primary influence is expression of, resistance of antagonism of the MC1R gene. (b) we don’t know how many copies of these genes exist (that I know of) or how many variable expressions are regulated, but it’s dominant. (c) there are really two regions that determine coloration. It’s the Black/Brown and the Blonde. The blond is from the Ancestral North Eurasians where we have genetics from around Lake Bikal I believe. (They’re gone, just integrated into us).

Black Hair:
MC1R Gene: In people with black hair, the MC1R gene typically functions efficiently, facilitating a high production of eumelanin. This creates the darkest hair shades.

ASIP Gene: The Agouti Signaling Protein (ASIP) gene can inhibit the MC1R function to some extent but usually doesn’t in the case of black hair. Efficient MC1R function ensures eumelanin dominates.

TYR, TYRP1, and DCT Genes: These genes are also crucial for the enzymatic pathway that leads to eumelanin production. Mutations or polymorphisms in these genes usually result in less effective eumelanin production and thus lighter hair.

HERC2/OCA2 Complex: The intronic SNP rs12913832 in HERC2 influences OCA2 expression, and a specific combination of alleles at this SNP is generally associated with darker hair colors including black.

Brown Hair:
MC1R Gene: In brown-haired individuals, the Melanocortin 1 Receptor (MC1R) gene usually functions normally, promoting the production of eumelanin over pheomelanin.

TYR, TYRP1, and DCT Genes: These genes are also responsible for the production and function of enzymes involved in eumelanin production.

SNPs: Various SNPs like rs12821256 have been associated with brown hair, usually increasing eumelanin synthesis or affecting its distribution.

Red Hair:
MC1R Variants: Variants of the MC1R gene are the most significant factor for red hair. These variants reduce the MC1R protein’s activity, leading to higher levels of pheomelanin.

RHC or Red Hair Color Alleles: Specific mutations like V60L, D84E, R151C, R160W, and D294H on the MC1R gene are known as RHC alleles and are commonly found in red-haired individuals.

Other Contributing Genes: Although MC1R is the primary determinant, other genes may also contribute to red hair color when mutated, though these are less well-understood.

Blond Hair:
KITLG and SLC24A4 Genes: These genes have been found to influence lighter hair shades, including blond.

MC1R: A normally functioning MC1R gene can also result in blond hair if other genes that contribute to lighter pigmentation are present.

SNPs: Various SNPs like rs1667394 in the OCA2 gene have been associated with blond hair.

Interactions and Modifiers:
Polygenic Traits: Hair color is polygenic, meaning it’s influenced by multiple genes interacting with each other.

Environmental Factors: Sun exposure and other environmental factors can also modify hair color over time, although these changes aren’t genetically mediated.

Sources:

“Genome-wide association studies identify several new loci associated with pigmentation traits and skin cancer risk in European Americans” by D. Liu et al., Human Molecular Genetics, 2015.
“Genetics of Skin Color Variation in Europeans: Genome-wide Association Studies with Functional Follow-up” by M.A. Visser et al., Human Genetics, 2014.
“Variants of the melanocortin 1 receptor gene (MC1R) and freckling among Hispanics” by E.J. Herraiz et al., Journal of the American Academy of Dermatology, 2016.