Originally Posted by hoodstar
I can't believe no one posted this yet but the hair loss gene comes from your mother, not from your father. It doesn't matter if your father is bald or your father's father is bald, it will not affect the potential of your hair loss. It is our mothers who carry the genes that indicates your possibility of hair loss.
chromosome: Simply put, the genes that determines one's traits.
First of all we must understand that a person is composed of a pairing of sex chromosomes. Our respective fathers have the chromosomes x and y, which indicate male, while in comparison, our mothers have two chromosome x's, indicating female. These chromosomes are important to know, as the hereditary hair loss gene resides from the x chromosome.
father (male) = [x,y]
mother (female) = [x,x]
When one is procreated, one chromosome from the father and the mother are required. Assuming the hypothetical baby is a male, he will need a designated "y" chromosome, only available from his father and to complete the set we must now acquire an "x" chromosome from the mother. However, there are two available which will complicate the process of identifying if the baby will turn bald or not.
How do we indicate if it the baby has the potential to bald, based on genetics?
The balding gene is a recessive trait located on our x chromosome, meaning that it needs to be paired with another x chromosome with the same balding trait for it to activate. However, if there is no available x chromosome to be paired with, it is immediately activated. This is why males are more likely to be bald than females. Females need two x chromosomes to turn bald as opposed to the male's one (as it needs to pair with a y chromosome). In retrospect, if your father is bald, this signifies that his only x chromosome has the trait pertaining to hair loss. If your father isn't bald, it means he has a dominant x chromosome.
We have just established that the father does not pass down the hereditary balding gene and this is why it is vital to look at the family tree of our mothers. Since the "y" chromosome was obtained from our father, we must now complete the set with a "x" chromosome. Since there are two "x" chromosomes available, we must look at the family tree from the mother's side to guess if one will turn bald or not.
legend:
x-r = recessive balding x gene
x-d = dominant x gene (no balding)
scenario 1:
father with luscious long hair[x,y] x doesn't matter here
bald mother[x-r, x-r]
Any male baby the couple will procreate will result in a bald baby as any x chromosome taken from the mother will result in the baby obtaining the balding gene.
scenario 2:
father with luscious long hair[x,y] x doesn't matter here
mother with hair [x-r, x-d] or [x-d, x-d]
Since the x chromosome is not activated we do not know if the mother has the recessive hair loss gene. There is a possibility that the mother has the recessive x chromosome but we do not know for sure. This baby can end up bald or with hair if the mother has the recessive x chromosome paired with a dominant x chromosome. To figure out if the mother is indeed [x-r, x-d] or [x-d, x-d] the family tree of the mother now has to be looked.
baby's mother [x-d, unknown x]
To figure out the other x, we must look at the father and mother of the baby's mother. Since females require TWO x chromosomes, one x chromosome from the mother and the father are required.
mother's father [y,x]
mother's mother [x,x]
Since we know that one of the gene is dominant (as indicated by the mother having hair) we must indicate if her mother or father has a balding gene or not. Since the father only has one x chromosome, we will know for sure if it is a recessive x chromosome or dominant x chromosome by his head. If he has hair, he has the dominant x chromosome and alternatively, if he is bald, he has the recessive x chromosome.
If the father is balding, we will know for sure that the baby's mother has a recessive x chromosome from her father. Since the baby's mother is not balding in this case, we know that a dominant x chromosome is required to deactivate the x chromosome, so we can safely assume the mother's mother gave a dominant x chromosome to the baby's mother.
mother's father [y, x-r]
mother's mother [unknown x, x-d]
..> baby's mother [x-d, x-r] + baby's father [y, unneeded x]
The baby's mother will have a chromosome pairing of x-r (from the father) and x-d (from the mother). Ta-da!
But.. if the father has a dominant x chromosome, we will not know if the x chromosome taken from the mother's mother is a recessive x chromosome or dominant x chromosome as the mother's mother can have either a pairing of [x-r, x-d] or [x-d, x-d]. This continues a tedious process in which we must now analyze the hair analysis of the mother's mother's parents (baby's great grandparents).
mother's father [x-d, y]
mother's mother if she has hair [x-r, x-d] or [x-d, x-d]
TL;DR
Hair loss is not caused solely on genetics but a number of contributing factors, including environment, health related issues, etc. Through science, we can analyze if one will turn bald due to the genetic make up of one's mother.
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