Crossing Over Question

Raquel Fialho nop43529 at mail.telepac.pt
Sun Dec 22 16:42:16 EST 1996

John Carroll <pp001356 at mindspring.com> escreveu:
> After checking assorted books on biology and biochemistry about
> how crossing over takes place during meiosis, I find myself still
> confused on a couple of points that an expert could undoubtedly 
> clear up without breaking a sweat.  Here are the points of confusion:
> 	1. In the diagrams of crossing over that I've seen, one segment
> 	   of DNA on the paternal chromosome is traded for its 
> 	   counterpart on the maternal chromosome.  I assume that
> 	   this actually takes place at many points along the 	   
> 	   chromosomes, rather than just the one shown in diagrams,
> 	   but I haven't seen any text to confirm that suspicion or 
> 	   any diagrams showing multiple crossovers.  Does crossing
> 	   over actually occur at many separate places on the 
> 	   chromosome?  If so, roughly how many segments are likely,
> 	   on average,to be exchanged per chromosome?  And roughly how
>            big are such segments, on average? 
> 	2. When DNA molecules are cut during the crossing over process,
> 	   are they cut only on linker strands (my guess) or only on
> 	   DNA attached to nucleosomes, or on both kinds of locations?
> The world's fate doesn't hang on answers to these questions, as you
> may have guessed, but they're driving me nuts.  All responses
> appreciated.  Thanks in advance.
> John Carroll
> pp001356 at mindspring.com

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