This is probably rather a small point, but I'd like to point
it out for scientific accuracy. In your article "Let's Talk about
Sex", they other guy talks about blood types. I believe he is entirely
wrong about it, though. Eye or hair color would have been a better
example. Some traits do have dominant and recessive attributes,
but not blood, at least not like was discussed.
It works like this:
For simplicities sake, we'll only consider blood type, omitting
positive or negative Rh factor. Thus, there is A, B, O and AB.
You have two genes to make up the type (one from mom and one from
dad). If you get an A from both, you have A type. Two B's, B type.
Two O's, O type. An A and a B, AB type. A or B are dominant over
O (or rather, O does not express and A and B do), so if you get
an A and an O, you have A type; B and O, B type. That?s it. If
you get an A and a B, you are AB. There is no recessive 'B' gene.
The types stand for the different types of antigens in ones blood.
O is the absence of either A or B antigens. In science class in
high school, we did tables of the chances of getting a particular
type given that of the parents.
For instance
One parent is AB, the other AO (or 'A' type). Thus, 50% chance
of offspring with type A, 25% AB, and 25% B. (Obviously other tables
possible with other combinations.)
Anyway, again, there is no recessive 'B' gene. If you have a gene
for B, then the B antigen will be expressed in your blood. Notice
that the only way to have type O blood is for both parents to have
given you the O gene ('O' means no expression of either the A or
B antigens).
As an aside, you can see that the best blood type to have is AB
positive, because you can receive blood from anyone. The universal
donor is O negative, with no antigens to muck up anyone else's
blood.
Eye color is a bit different. If one parent has brown eyes and
one blue, you'll likely end up with brown-eyed kids. They have
one gene for blue eyes, but the brown gene is dominant. Not that
you can't have a blue-eyed kid in this case (brown-eyed parent
has one blue gene, blue-eyed parent has both blue genes). If you
have two blue-eyed parents and the kid has brown eyes, that's when
a test for paternity is needed.
All of this is from remembered high school classes, and it has
been a long while since I've gone, but my wife remembered the same
thing and she went to a different high school than I did.
Not sure that any of this has a bearing on your Sex discussion,
but it bugged me to see the blood-gene stuff wrong.
David |