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Nicole_5521
#1 Posted : Tuesday, May 25, 2021 9:52:14 PM
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Hello,

I'm a little confused about how distance between genes affects crossing over.

How come in terms of meiosis, when 2 genes are closer together (smaller distance) they are more likely to cross over in prophase I (pg. 87 Lesson 1.2A of Prep101 book).

However, in terms of crossing over/linkage, in Lesson 1.2B, it discusses the scenario where if A1/B1 and A2/B2 are closer together, then they'd likely not cross over. And if A1/B1 and A2/B2 are far apart, then crossing over is likely to happen.

So why does it seem like it's different in meiosis vs. the crossing over/linkage example? Are they 2 separate concepts?

Thanks so much!
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INSTR_Kennedy_135
#2 Posted : Thursday, May 27, 2021 5:56:29 PM
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Hello!

You are spot-on that in meiosis (prophase 1) genetic recombination occurs. It makes sense that the closer the material is the more likely they would cross over (even just from a statistics perspective). This allows more genetic variation for the next generation!

Crossing over/linkage refers to the extent of genes on the same chromosome being inherited together and this is indirectly proportionate to the distance separating them. If 2 genes/loci are linked it is unlikely they will cross over or recombine to different combinations (they will stick together in the population), whereas if they are unlinked it is a higher likelihood you will get different combos.

I think you have a good grasp of each- have confidence in your knowledge!

Kennedy
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Nicole_5521
#3 Posted : Friday, May 28, 2021 4:06:44 PM
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By being indirectly proportionate to the distance separating them, does that mean if 2 genes are closer together, they would be more likely to be linked? If so, would that mean they would be less likely to cross over?

If this is the case, how come during meiosis, it is more likely for genes to cross over if they're closer together? Because wouldn't gene linkage also be occurring simultaneously in meiosis?

Thanks!!
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INSTR_Kennedy_135
#4 Posted : Tuesday, June 01, 2021 2:27:47 PM
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Nicole,

I wouldn't get too bogged down in the details. Crossing over in meiosis in molecular genetics (individual level) is more likely to occur when genes are closer together (and this helps with genetic recombination). Crossing over/linkage in population genetics refers to the likelihood 2 genes will stay together in prophase 1 (on a population level) based on how close they are on the chromosome. If 2 genes are far on a chromosome they will likely cross over and recombine for various gene combos (more genetic variation) vs just staying together and always being inherited together in a population (getting the same trait the same way across the population).

Hope this helps.
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