Sex-ratio in Siamese twins.

Paul Kemp pkemp at byron.u.washington.edu
Fri Mar 5 15:51:34 EST 1993



I heard an interesting fact the other day, and don't have a good explaination
for it.  80% of Siamese twins are female.  Does anyone know why this is true?

I am assuming that Siamese twins are identical twins.
I believe the sex-ratio in identical twins is pretty close to 50:50

Possible causes:

1. Male Siamese twins die before they are born.
2. Females are pre-disposed to incomplete fission.
or 3. (the interesting one) Some Siamese twins are XY, but due to incomplete
      development they never obtain male characteristics.

Anyone have any ideas?
pk
pkemp at byron.u.washington.edu



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