Naked Science Forum
Life Sciences => Physiology & Medicine => Topic started by: another_someone on 07/02/2006 23:56:23
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I was just wondering if there was a gender bias in babies born with genetic defects.
Logically, aside from sex chromosome errors, the number of genetic errors at conception should be the same, but that does not mean that an equal number will be born – it is always possible that one sex has a greater likelihood of aborting a foetus containing a genetic error than would the other sex.
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more males are spontaneously aborted than females. Or so my Human Growth professor tells me
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Originally posted by elegantlywasted
more males are spontaneously aborted than females. Or so my Human Growth professor tells me
But despite that, slightly more males are born than females. That must imply a significantly greater likelihood of conceiving males.
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Is the spontaneous abortion thing to do with boys being more likely to be rejected by the mother's immune system (like the blood group thing?)
I think I heard more males succumbed to infant mortality too...
But then, some at least of that is probably due to the sex-linked issue of men only having one X chromosome so not having cover against problems in those genes... the question suggests excluding "sex chromosome errors" but I rather doubt that's possible. There are probably loads of other factors but it's hard to tell what their relative importance would be...
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Originally posted by rosy
I think I heard more males succumbed to infant mortality too...
But then, some at least of that is probably due to the sex-linked issue of men only having one X chromosome so not having cover against problems in those genes... the question suggests excluding "sex chromosome errors" but I rather doubt that's possible. There are probably loads of other factors but it's hard to tell what their relative importance would be...
I too had heard that more males die at every stage of life than females, even in the first few years, but I have not heard anything about it being linked to the X chromosome (which also means I have not heard anything to the contrary).
The reason I asked the question in the first place is just one of those ideas my mind was trying to think through, and it seemed a logical conclusion that males should be expected to be born with a higher rate of mutations than females.
The reasoning that brought me to this speculation is that in most species, females are almost guaranteed to be able to mate, and although the quality of male they might find to mate with may vary, the probability of being able to reproduce appears to be fairly constant. On the other hand, the likelihood that a male is able to mate is highly variable, and some males have many mating opportunities, while others seem to have very few, or none at all. It would then imply that natural selection would be applied more powerfully upon males than on females, and thus it would make sense that males should have more random mutations in order that selection might be applied to such selections, while if the same level of random mutation were to develop in females one would expect a more indiscriminate transmission of that mutation into the next generation.
The idea was mere idle speculation, and may be total rubbish, but I was just curious if there was any statistical evidence consistent with the idea.
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Also just to complicate things if i may, percentage wise the largest group which suffer genectic defects are children born through IVF.
Michael
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Swift explanation of the x-chromosome thing...
Females have two x-chromosomes. Men have only one.
The y-chromosome has few active genes and they're mainly involved in male-reproductive stuff.
The x-chromosome is large and has many important genes on it. For normal chromosome pairs if there is a recessive fault on a gene, it will be covered up (more or less) by the normal gene on the other chromosome (which is why sickle cell anaemia, cystic fibrosis, etc really only appear in the presence of two faulty copies).
x-chromosome genes are different as any cell has only one active x-chromosome, but in women there are two seperate chromosomes and they're each active in 50% of cells so many errors are covered up for (as in haemophilia, and I think at least one form of muscular dystrophy) whereas men only have one copy so any faulty gene mean that no good protein is made for that gene.
Thus, some of the tendancy toward males dying early might be explained in terms of faults, not necessarily detectable, on the x-chromosome which would be non-fatal in the female.
There are inevitably any number of other reasons, but that was what I was suggesting.
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quote:
Is the spontaneous abortion thing to do with boys being more likely to be rejected by the mother's immune system (like the blood group thing?)
Im pretty sure the Rh factor can affect both male and female zygotes equally, its just dependant on the +/- factor of the father.