Date: Mon, 26 Apr 1999 19:52:55 +0000
From: Marc Afifi <mafifi@redshift.com>
To: Pinhole Listserv <pinhole@exploratorium.edu>
Subject: Re: sibling probabilities
Forgive me chiming in, but we're working on number two.
Doesn't the sex of the offspring probability depend on the composition
of the sperm? I seem to remember an ovum only contains the X chromosome
and sperm can be X or Y. If the sperm composition is 50% X and 50% Y
then the probability of the sex of any offspring is 1/2. The chance of
having a boy or girl should be 50-50 no matter what number they are in
the sequence of siblings (much like rolling dice, each roll is an
independent event and not related to the prior roll). On the other hand,
the chance of having two boys or two girls is not 50-50. The chance of
either two boys or two girls is 1/4, total 50% for both possibilities,
leaving 50% chance of boy girl or girl boy. What am I missing?
-Marc