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>