You've probably heard people say that if your mother's father was bald you're more likely lose those beautiful locks of hair down the road.
你可能听说过，如果你祖父秃头，那你也很可能会秃。
But what truth is there to this?
但为什么呢？
It turns out that one of the major contributors to hair loss is sex linked.
事实上，其中一个导致秃头的原因与性别有关。
Humans have forty-six chromosomes of DNA, of which two help determine your sex, the "X" and the "Y" chromosome.
人类 DNA 有 46 条染色体，其中两条决定你的性别，X 与 Y 染色体。
If you're a female you have two "X" chromosomes, but if you're a male you have an "X" and a "Y" chromosome.
女性拥有两条 X 染色体，而男性拥有一条 X 染色体与一条 Y 染色体。
Studies show that the most influential hair-loss gene is located on the "X" chromosome only.
研究显示造成秃头的基因位于 X 染色体上。
What does this mean?
这代表什么？
Well if you're a male you get an "X" chromosome from your mother, but must receive a "Y" chromosome from your father.
男性会从母亲那得到其中一个 X 染色体，但是一定会从父亲那得到 Y 染色体。
Because if you got your father's "X" chromosome you would be a female.
因为如果是从父亲那得到 X 染色体，那你就会是女性。
So if one of your mothers "X" chromosomes has this hair loss gene you have a 50/50 chance of getting it from her.
如果母亲的其中一个染色体有秃头基因，你就有一半的机会秃头。
In this way, hair loss is partially hereditary and passed through the maternal side for males.
因此对男性来讲，秃头基因是由母亲遗传决定的。
Females, on the other hand must get two copies of this gene, one on each "X" chromosome in order to physically express it.
而女性则必须得到分别位于两个 X 染色体上的秃头基因才会秃头。
So if your mother does express these traits it means she will be passing an affected "X" chromosome to you.
因此如果你的母亲秃头，你就一定会得到秃头基因。
But why do we say to look at your mother's father?
但是为什么是要看祖父有没有秃头？
Well, if he has visible male pattern baldness then your mother has at least one copy of the affected "X" chromosome from him,
因为如果祖父秃头，你的母亲至少会有一个秃头基因。
because in order to have a daughter he must have passed on his "X" chromosome, not his "Y".
因为女儿一定会得到父亲的 X 染色体，而不是 Y 染色体。
The thing to note here is that this is just one of the contributors to hair-loss and while its thought to be the most significant,
虽然这被认为是最重要的因素，但这只是许多造成秃头的因素之一。
many studies have found other hair linked genes which aren't sex-linked at all.
许多研究指出，其他造成秃头的基因与性别无关。
Including some on the "Y" chromosome, meaning they can be transferred from both the mother and the father.
其中包含一些在 Y 染色体上的基因，也就是说父母都有可能是你秃头的原因。
On top of this, some studies have shown correlations between age, exercise, nutrition and even stress levels.
另外，研究指出其他因素，譬如年龄、运动、饮食，甚至压力都有影响。
So while a quick check of your mom's dad's hair may be an indicator for future hair loss, a head full of hair on Grandpa's head does not guarantee you are in the clear.
所以当你察看祖父是否秃头时，也许可以预判自己未来是否也会秃头。但是就算祖父头发很多，也不保证你能保持头发茂密。
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