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We had to ask a question on Friday, and now we have to make a 3-5 minute speech on the answer..
My question was: Why are people's hair colors only blond,brown,red, and black?
And I have to have a visual aid. I think I have that covered, but ideas are loved.
I've been searching FOREVER for the answer to my question, but i'm only coming up with WHY we get those hair colors, not why those are the only ones people have.
It all goes back to genetics.
Hair color is controlled by multiple genes.
Here is a pretty quick genetics lesson. I gave this lesson to another person on a different forum, so I have the pictures and everything for this:
This is a Punnett Square for two crosses between a tall pea plant and a short pea plant.
TT is a homozygous tall. That means that the alleles it recieved from it's one parent was a dominant T allele and the other was also a dominant T allele.
Tt is a heterozygous tall. That means that the allele it received from one parent was dominant and the allele it recieved from another parent is recessive. It is still tall, because the dominant allele overshadows the recessive.
Hair color has many genes that control it.
One theory is the three-gene model.
This states that:
One gene is a dark brown/light blonde gene. In it, the dark brown allele overshadows the light blonde allele, similar to how the tall allele in the pea plant overshadowed the short one. So, even a person with a light blonde recessive allele that also has a dark brown dominant allele will have dark brown hair. This also explains why if a brown haired man and a brown haired woman marry and have a child, the child can have blonde hair. It is because the recessive alleles in the heterozygous parents cross. There is a 25% chance of this.
Another gene that controls hair color is the red hair gene. It is similar to the albinism gene. There are two alleles, one is basically an allele that stops the production of pheomelanin, I believe (correct me if I am wrong). Pheomelanin brings the red pigment of the hair. The red-stopping allele is dominant and the allele that doesn't stop production of pheomelanin is recessive. The reason why people have different shades of red is because of the brown/blonde gene.
I believe there is also a black hair gene. I believe that if you have it, it will overshadow all the preceding genes, unless you have are dominant in the brown hair gene...and you will 100% have the gene that stops the pheomelanin in the red hair scenario. If you are dominant in brown hair, then I think you'll have a dark brown/blackish color.
Also, I am a genetics god. If you have anymore questions post, and I will get back to you
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