[PW] ? DNA question

[John Franklin]

On Jan 14, 2008, at 12:49 AM, Peter Macinnis wrote:

> John Franklin wrote:
>
>> (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...)
>
> I don't think that is right, John.  See the human karyotype at
> http://homepage.mac.com/wildlifeweb/cyto/human/HSA550.gif

Ah, well, that's why I shouldn't try to reply to the list when I have  
a cold in the head -- it knocks everything else out. But thanks for  
not letting the inaccuracy stand pat. ;)

Yes, we have 23 PAIRS of chromosomes, and each PAIR is X-shaped. The Y  
shape comes in when you put X and Y together. I seem to recall  
reading, though, that X and Y names do come from the shapes -- since Y  
has a stub where X has a full leg (arm? stem? whatever), an XX pair is  
X shaped, while an XY pair is not-quite-Y shaped. Even if this is an  
after-the-fact explanation, I hold that the professor's comment refers  
to this, and not to a question of parentage.

Serves me right for calling someone else ignorant. Now, if you'll  
excuse me, I have sneezing to do.

-John Franklin