Questions re crossing over and histones

[dawn1070]

A question I encountered is asking to demonstrate using a diagram of a bivalent of the F1 progeny with a single crossing over event causing all the produced gametes to be parental? I don't get how this works because I thought crossing over would have resulted in recombination no matter what?

Also why do prokaryotes not have histones surrounding their chromosome? I thought it was because there was only one chromosome, therefore space/tangling are less of an issue.

[JackBean]

histones probably evolved later. However, to my knowledge, they have some histone-like proteins.

You could have also double crossing-over. Or crossing-over on other chromosome

[dawn1070]

histones probably evolved later. However, to my knowledge, they have some histone-like proteins.

You could have also double crossing-over. Or crossing-over on other chromosome

I'm looking at the question now and it is asking for a single crossing over event.

What do you mean by crossing over on other chromosome?

[fastsandslash]

Ahh.. right. Most prokaryotes have a single loop of DNA, and we all know how hard it is to wind a rubber band (chromosome) around a ball (histone) and utterly pointless as yes, it only has 1 chromosome. Try unwinding it for protein synthesis... *shudders* I mean, good luck. Well, I'm quite sure JackBean was meaning, how about the *other* chromosomes crossed over, but *these* chromosomes are still the same as before . Assuming that parental means identical to parent chromosome, then my best bet would be that the alleles that recombined were identical in both parents (nigh impossible). So... uh. Yeah.