[PW] ? DNA question

[Roger Post]

The professor should be fired or at least shot.

There can only be one sperm that fertilized the egg. Sex is determined by a 
separate pair of  Chromosomes 
http://biology.about.com/library/weekly/aa091103a.htm  Normally the female 
has two X Chromosomes and the male has an X and a Y.
So the young lady should have had two X Chromosomes or she would have been a 
guy.  But we all know that there are some very rare occasions when things 
are not normal.

Most mammals have one pair of sex chromosomes in each cell. Males have one Y 
chromosome and one X chromosome, while females have two X chromosomes. In 
mammals, the Y chromosome contains the gene that triggers embryonic 
development as a male. This gene is SRY. Other genes (in addition to SRY) on 
the Y chromosomes of men and other mammals are needed for normal sperm 
production.

There are exceptions, however. Among humans, some men have two X's and a Y 
("XXY", see Klinefelter's syndrome), or one X and two Y's (see XYY 
syndrome), and some women have three Xs or a single X (and no Y, "X0", see 
Turner syndrome). There are other exceptions in which SRY is damaged 
(leading to an XY female), or copied to the X (leading to an XX male). For 
related phenomena see Androgen insensitivity syndrome and Intersex.

The above paragraph came from http://en.wikipedia.org/wiki/Y_chromosome  And 
Wikipedia is not my favorite source but the nice think is that is has links.

None of the different combinations as far as I know are the result of two 
sperm cells fertilizing the egg. I have no idea what the professor was 
trying to tell the young lady but she probably will find out if the class 
goes into this kind of think.  If not then she probably should take the 
results to her regular doctor and have him explain to her what the professor 
was talking about.




----- Original Message ----- 
From: "Mary Barna" <mbarna at albright.org>
To: "Project Wombat" <list at project-wombat.org>
Sent: Saturday, January 12, 2008 7:21 PM
Subject: [PW] ? DNA question


>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.
>
> ******************************************************
> Mary Barna, Director
> Valley Community Library
> 739 River Street
> Peckville, PA  18452
> phone (570) 489-1765  fax (570) 383-9657
> email -- mbarna at albright.org
> webpage -- www.lackawannacountylibrarysystem.org/valley
>
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