[PW] ? DNA question

[John Franklin]

On Jan 12, 2008, at 6:21 PM, Mary Barna wrote:

> A patron had a second-hand question that she would like clarification
> on.  I will try to explain it to the best of my ability.  She said  
> that
> her sister, in a college class, had a DNA sample taken.  When the
> results were in, the Professor made a crack in front of the class that
> her DNA had one female strand and two male strands (or lines?) and she
> should "go home and talk to your mother."  The kid was devastated,  
> since
> her parents divorced partly because her father was not sure if he was
> her father. (He is!)
>
> The implication, that mom had sex with two guys that impregnated her  
> one
> egg, doesn't seem legit to me.  I have heard of fraternal twins having
> different parents, but could this be a fact in this case?  It's an odd
> question, I know.

Actually, this sounds like a "we can't stand Pat" story* -- maybe it's  
the fact that I have a head cold and am not thinking normally as a  
result, but I think I understand the comment and I don't think that  
the professor was saying she was XYY, which would make her, as Mr.  
Macinnis has pointed out, male. He was trying to imply that she was so  
masculine that one of her Xs was acting like a Y with an extra tail,  
meaning that he was trying to mock her for being a masculine female.  
(For those who haven't picked it up from this thread, let alone other  
sources, the X and Y chromosomes get their names from their shapes;  
the "X" shape is the normal one for a chromosome, but the Y is missing  
a leg...)

There is no way to tell by looking at a person's DNA, without samples  
from their parents, whether they are illegitimate or not. (Like the  
"evil bit" in IP packets, there is no "illegitimate gene".) And  
there's no way that a college professor would fail to know that XYY  
humans are male -- that's basic enough to have made it into Larry  
Gonick's Cartoon Guide to Genetics. Besides, it's highly unlikely that  
a college professor would bother to dig deep enough into his students'  
backgrounds to know enough about her to make such a crack deliberately.

(And yes, if I'm right, this still means he's a terrible jerk and she  
can feel free to resent him. It just means he isn't a jerk who is  
ignorant of genetics.)

*From a letter published in one of Scott Adams' Dilbert business  
books. A guy said to his staff that while things were getting better,  
they still couldn't stand pat. He was later asked why he hated  
Patricia so much as to publicly insult her...

-John Franklin