you "can't" carry a baby of that gender!
How many times have we heard THAT one? :confused:
For those of us with a lot of one gender and none of the other, well-meaning friends and relatives may chime in with that helpful tidbit, implying that for some medical reason, it's actually IMPOSSIBLE for us to conceive or carry to term a child of our desired gender. But how true is it?
Like many old wives' tales, this actually does have a basis in fact. Some women carry certain genetic diseases, like hemophilia or Duchenne muscular dystrophy, on one of their X chromosomes. Everyone has one X chromosome, but women have two. Because of this, if a woman has one bad X and one good X, the genetic data in the good X allows her to develop normally. However, she'll always carry the bad genetic information on her other X chromosome.
Until she has children, she may never even know she carries a defective X chromosome. And if she had all daughters, she still probably would never know, because females get one X from their mother, and one X from their father, so the odds are good that one or the other of these X's will be normal. Some of her daughters will carry the bad X chromosome and some won't, but none of them will develop the disease because they all got at least one good X.
If she has sons, however, then the situation becomes more complicated. Depending on which of their mother's X chromosomes they receive, sons of a woman who carries an X-linked disease can either be perfectly fine (they received a good X from their mom and then their dad's Y chromosome) or they will have the bad X and suffer from the disease. Because they only HAVE one X, they have nothing to fall back on, and they will get sick. If a woman carries one of these diseases, all her daughters will be perfectly healthy (half will be carriers) and half her sons will be healthy, statistically speaking. It's really the luck of the draw which X your children will receive.
Technically, girls CAN get these genetic diseases. But in order to do so, they have to have both parents who carry the disease on their X chromosome, and since the disease will manifest itself in their father, if your husband doesn't have any X-linked disease, the odds are pretty much 100% that his X chromosome is sound and even if you are a carrier of one of these diseases, your daughters would never develop them. If he does have an X-linked disease, it's a very mild one. Otherwise he would be visibly sick or dead.
While Y-linked genetic defects do exist, they are very mild. An excessive amount of hair on the ears is an example. If Y-linked disorders caused serious disability, men who carried them would be incapable of fathering children and the mutation would not survive to be handed down from generation to generation. The reason why X-linked diseases exist despite being severe is because females are unaffected carriers, so the genetic mutation survives from one generation to the next. Only males who inherit their mother's one bad X chromosome will ever develop the disease.
Some X-linked diseases are chronic conditions like hemophilia, where a boy can manage the disease their entire life and still have a pretty normal existence. But others cause fetal death in utero or very early on in childhood. If you have a large number of healthy daughters, and have miscarried repeatedly (even if you don't know the gender of the child), you may want to consult with a genetic counselor to rule out the possibility that you carry one of these genetic disorders.
If you are a carrier, you may see a trend in your extended family of more daughters than sons being born, or mysterious cases where a baby boy was born, had developmental delays, and died at a young age. It's not always easy to tell, because doctors really didn't always know why people died even as little as 20 or 30 years ago and so may have attributed deaths to incorrect causes.
If you see such a pattern in your family (it will be on your mother's side), even if you have only one or two daughters or all sons and have never miscarried, you also may want to consult with a geneticist. Remember that it's sheer luck which of your X chromosomes your children receive, so even if you have 5 sons and they are all healthy, if you carry an X-linked disorder, you could still pass down that gene to your next son.
Most of these diseases are extremely, extremely rare. It is very unlikely that you are a carrier, even if you have 10 daughters and no sons. And it is impossible if you have 10 sons and no daughters, because it's NEVER impossible to carry daughters, due to girls having two X chromosomes. So when your neighbor peeks over the garden gate and tells you that you "just can't carry" girls or boys, just ignore him or her. The facts tell a different story.
