I was wondering how this works as I’ve read up on it but I am still very confused. I am 20 and have a full head of hair. My father who is 54, also has a full head of hair but it is fine to where I can see his scalp. He also has a receding hairline. My fathers father has a full head of hair and he is 82 but had the same type of hair as my father. My mothers father has a full head of good hair and his father did too. BUT my grandmothers from my mothers side and my fathers side both had fathers that were bald which worries me a lot. Does this mean I will go bald or do I only need to look at my mothers fathers hair to know if I will go bald or not.
Thank you so much.
In: Biology
As with a lot of genetics, there are no certainties, only probabilities. (Male) baldness is determined by a number of genes, and for each gene there is a 50:50 probability of being passed down from one generation to the next.
First the slightly simplified story, which is about a single gene on the X-chromosome. This gene, with the prosaic name of “AR” is associated with a doubled risk of baldness, compared to individuals who do not have this gene. There are a few more “baldness genes” on the X-chromosome, but for simplicity let’s focus on AR, which seems to be most strongly correlated to baldness. Because this gene is on the X-chromosome, as a man you can only get it from your mother (since your dad gave you a Y-chromosome). But your mother has two X-chromosomes, one from her dad and one from her mom. So it’s not the case that you can only get this gene from your mother’s father – you could equally well get it from your mother’s mother.
So why do people say to look at your mother’s father, and not her mother? Well, because this is about male baldness. Women can also go bald, but less commonly than men and with different genes involved. So, your mother’s mother might very well have the AR gene, and you might have inherited it from her, but there’s no way to tell by looking at her if she has AR, because she’s unlikely to be bald with or without it. Your mother’s father, on the other hand, is more likely to be bald if he has the AR gene. But it’s not a sure thing. He could have a full head of hair but still carry the AR gene. Or he could be bald without the AR gene. So if your mother’s father is bald, all it tells you is that he has an increased probability of carrying the AR gene. And even then, it’s not a given that this gene was passed on to you.
If your maternal grandfather does have the AR gene, then he definitely passed it on to your mother (since it lives on the X-chromosome, and your mother, being a woman, must have one X-chromosome from her dad). And then there’s a 50% chance that your mom passed it onto you (since you could have inherited either one of her X’s). If your maternal grandmother has AR, there’s only a 25% probability that you inherited it from her, so that relationship is also less strong, which is another reason to look at your mother’s father rather than her mother.
In summary, there really isn’t all that much information to be got from looking at your maternal grandfather’s scalp. If he’s bald, all it tells you is that your probability of having an X-linked baldness-promoting gene is somewhat increased. But it’s not certain that you have it, and even if you do, not everyone with AR (or another X-linked baldness gene) goes bald.
In addition, as I said there are many more genes involved in baldness, and only some of those are on the X-chromosome. Those that aren’t on the X-chromosome can be passed on from either your mom’s or your dad’s side of the family. It’s worth noting that more than [80%](https://www.ncbi.nlm.nih.gov/books/NBK278957/) of people experiencing baldness had a bald or balding father, which suggests that it may be better to look at your dad’s side of the family.
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