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Archiver > Scotch-Irish > 1998-08 > 0904444573


From: "Katharine Kirk" <>
Subject: Re: Blood Types vs Genealogy
Date: Sat, 29 Aug 1998 21:36:13 -0500


>From what you tell me here, your father had two B genes and your mother had
one A gene and one B gene. Your father had only a B to donate to any child.
Your mother had one of each. So the children could be B or AB with a 50:50
chance either way. So you have a 50% chance of being what you are a B.
Your father was Rh +, so he was either a ++ or a +- genotype. Your mother
was Rh negative so she had to have been a - -. Since you turned out to be
Rh - yourself, we can assume that your father was heterozygous for Rh, that
is, he had one + gene and one - gene. That is the only way you can be Rh -.
The probability of a Rh negative child in this situation is again 1/2. The
probability of all three out of three children from a couple with this gene
configuration being Rh negative is 1/8. Or if you meant that there were
four children and the second one was Rh+, but you and the other two were Rh
negative, the probability of that happening is 1/4. So your family's
results are not out of the ordinary.

You are right about the data being a bit skewed prior to the introduction of
the vaccine (and of the transfusions used before the vaccine was available),
however, because the children of Rh negative mothers who were not also Rh
negative tended to die soon after birth. If only the types of the living
children were known, it could appear that the frequency of Rh- was
increased.

Regards,
Kathy Kirk

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