Thread by @BayerischerWolf

Europe has all the diversity it will ever need. #WhiteGenocide will only result in the destruction of all this beauty in favour of a melanin-saturated and low IQ mutt population.

@Commodore_1853 requested last month that I make a thread similar to my XX/XY chromosome thread, but about eye and hair colour inheritance, and their respective genes. I will do so to provide insight into these endangered phenotypes.

https://twitter.com/Commodore_1853/status/998622813123694593

1. The colour of our hair and eyes originates from a pigment substance known as melanin, which comes in two variations: eumelanin (which itself comes in two variations, black and brown), and phaeomelanin (a reddish pigment).

2. The production of melanin is regulated by the MC1R which is found on chromosome 16. MC1R produces a receptor known as melanocortin-1.
> Eumelanin is produced when the receptor is activated
> Phaeomelanin is produced when the receptor is disabled

3. Most red hair derives from a mutated MC1R gene that causes the production of red phaeomelanin instead of eumelanin in hair colouration. This rare gene is recessive, meaning, both parents must give their child this gene in order to have a ginger child.

3. cont. However, both parents DO NOT have to have red-hair to have a child with red-hair, provided that both of them are CARRIERS of the gene. In other words, one of their two pairs of chromosome 16 has the gene, but since it is recessive, it does not express/activate.

3. cont. For example, in the Punnett square below, both parents have non-red-hair, but are carriers for the mutated MC1R gene (Rr), where R = wild-type (normal) M1CR gene, and r = mutated M1CR gene.
> In this situation, the couple has a 25% chance of having a red-haired child

3. cont. If both parents have red-hair, then they have a 100% chance of having a child with red-hair (provided no other abnormalities exist in other genes).

3. cont. If one parent is a red-head, and the other is a non-red-haired commoner, then the chances of a child having red-hair will depend if the non-red-haired parent is a carrier or not.
> If yes, then there is a 50% chance of a child having red-hair
> If no, then no.

4. In truth, one has to think of red-hair as a different category (the phaeomelanin category) of hair colour compared to brown-hair (eumelanin category). It has its own shades of light and dark, and with it, different variations of the red-hair gene also contribute to...

4. cont. ... other phenotypes, such as freckles and pale skin. Of course, mixture does and can occur between the eumelanin and phaeomelanin groups, but I will talk about these hair-colours (auburn and strawberry blonde) after I talk about the eumelanin hair-group.

5. The eumelanin hair-group consists of the shades of hair from black-hair to light-blonde-hair, where the overall production of eumelanin is responsible. No specific gene has been specified to be the main contributing factor in this. The topic is massively under-researched imo.

6. Genes that code for darker hair will typically be dominant over lighter hair.
> black hair results from a dominance in black eumelanin production
> dark brown hair results from a dominance in excessive brown eumelanin production

6. cont.
> medium brown-hair results from a dominance in medium-level eumelanin production
> light brown-hair results from a dominance in a low-level of brown eumelanin production
> blonde hair results from a dominance in a very low-level of brown eumelanin production

7. Black hair is typically a dominant trait. So, like with red-hair, if a parent with black-hair is a carrier for another type of hair colour (such as blonde hair) there may be a chance that with a partner that is blonde, the child of this couple may come out blonde.

8. Brown hair is dominant over blonde hair, but recessive to black hair. Again, this doesn't mean that just because one parent is black-haired, the child will also be black-haired (even if both parents are black-haired).

8. cont. In the Pundett Square below, B = black-hair and b = brown-hair. Both parents are black-haired, but carriers of brown-hair genes. I've listed the respective genotype and phenotype percentages in the next picture.

8. cont. In the Pundett Square below, B = black hair and b = brown hair. One parent is black-haired (purebred) and the other is brown-haired purebred. The results here are simple: there is a 100% that the child will be black-haired, but a carrier to the brown hair trait.

9. Blonde hair is the most recessive trait, but like red hair, it's possible to have blonde hair even if both your parents are brown, or even black haired if the parents are at least carriers for the gene.

Two blonde-haired parents have a 100% chance of having a blonde child.

10. Strawberry blonde hair is what happens when you have one parent with a recessive blonde gene and another parent with the recessive red-head gene.

10. cont. Although technically, red hair is dominant over blonde hair, the shades are so light, the light amount of eumelanin and phaeomelanin mix to give the beautiful shade of hair below.

11. Eye colour is a little better understood than hair colour (both in turn are better understood than skin colour). The same pigments are at play, but they each reside in two separate locations in the iris: the anterior stroma and the posterior epithelium.

11. cont. The two different layers and melanin levels will be responsible for the differing eye colours. There will also be different genes, such as the HERC2 gene responsible for most cases of blue eyes in Europeans, which inhibit melanin placement in certain parts of the eye.

11. cont. side note: Black melanin has no role in eye colour. There is no such thing as black eyes, and what is usually described as 'black eyes' is usually just very dark brown eyes.

12. Brown eyes are produced by a combination of brown eumelanin in both the anterior and posterior layers of the iris, where there is a larger amount in the anterior stroma than the posterior epithelium.

12. cont. The genes behind brown eyes are dominant in addition to being the most common. Variations of the gene are responsible for light brown eyes and darker brown eyes.

13. Blue eyes are produced by a combination of eumelanin in the posterior layer of the eye, and no melanin in the stroma. In Europeans, the mutated version of the HERC2 gene is responsible for this absence of melanin in the stroma.

13. cont. Blue eyes are blue for the same reason as the sky. The absence of melanin to absorb light in the stroma means that short light waves will instead reflect back, and this gives the blue appearance in people (such as myself).

It makes the compliments like, "You've got eyes as beautiful as the sky," or metaphors like "sky blue eyes" that much truthful. 😅

14. The HERC2 mutation ONLY works if both chromosomes carry the mutated one, which means, it's recessive. If your mutated HERC2 isn't allowing melanin into the stroma, then your other one will. If both can't then you're going to get blue eyes (provided no other genes interfere).

14. cont. side note: another reason why you could have blue eyes, is if you have a mutation in your OCA2 gene. Although, most Europeans have it for just the HERC2 gene (and sometimes both) so it didn't seem relevant to add.

15. The inheritance of blue eyes works much like blonde hair, in that you need two genes from both parents to ensure that blue eyes will be expressed instead of brown eyes.

15. cont. For example, two parents that have blue eyes have a 99.9% chance of having a child with blue eyes. The 0.01% is the rare case a new mutation forms, or there is a recessive trait that will cause these eyes to turn green instead, etc.

Shit happens.

15. cont. The second scenario to get blue eyes, is if one parent has blue eyes, and the other is a carrier for blue eyes (i.e. they had a parent with blue eyes, but they came out brown themselves). In this case, there is a 50% chance a child may come out with blue eyes.

15. cont. The third scenario to get a blue-eyed child, is if both parents are recessive carriers of the trait and they breed together. There would be an approximate ~25% that the child will come out with blue eyes.

16. Green eyes are a bit more complicated. They involve the same mechanism that makes blue eyes blue, but the dominant pigment here is phaeomelanin instead of eumelanin. There is also the involvement of a substance known as lipochrome, which comes from a entirely different gene.

16. cont. Green eye inheritance is (again) complicated. They're like the red hair of eye colour. They're recessive to brown eyes, but dominant over blue eyes.

16. cont. Two parents with green eyes will, like blue-eyed parents, have a 99.9% chance of having a green-eyed child.

17. The complications begin with one parent being blue-eyed and another being green-eyed. Since green eyes aren't understood very well, all we know about them is that they're a multi-allele trait, so anything could happen.

17. cont. It even caused me to scratch my head since I had a parent with green eyes, and I came out with blue! So, I did some extra research, and the rule of thumb is that it'll be a 50/50 odd for the child if one parent is green-eyed, the other is blue-eyed.

17. cont. If a parent has brown eyes and mates with someone that has green eyes, then the statistical chance that the child will have green eyes will depend on the status of the brown-eyed parent.
> carrier for green, then 50/50 for green
> not carrier, then 0.01% for green