Kaplan FL 5 #10 Bio section

[akimhaneul]

So why can't the answer be 70%? I got CDAB.

Why can't the recombinant frequency be greater than 50%?

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[betterfuture]

Good question. There seems to be a bit of confusion about what recombinant frequency is so let me explain.

Recombination frequency deals with how close together genes are. They will stay together through recombination events if they are close to each other. That is, if they are on the same chromosome. Tightly linked genes have a recombinant frequency close to 0% and weakly linked genes have a recombinant frequency close to 50%. You can't have a percentage higher than 50% - that just means it is random chance. From the answer choices, you should be able to eliminate any percentage higher than 50% leaving you with C.

 

[theonlytycrane]

Good question. There seems to be a bit of confusion about what recombinant frequency is so let me explain.

Recombination frequency deals with how close together genes are. They will stay together through recombination events if they are close to each other. That is, if they are on the same chromosome. Tightly linked genes have a recombinant frequency close to 0% and weakly linked genes have a recombinant frequency close to 50%. You can't have a percentage higher than 50% - that just means it is random chance. From the answer choices, you should be able to eliminate any percentage higher than 50% leaving you with C.

This has always confused me, I'm not sure why. I think when I first heard about recombination frequency, I saw the definition as # of recombinant offspring / # total offspring. I thought that if all offspring were recombinant, the frequency would be 1. It sounds like you're defining it in terms of how likely it is for a recombination event to occur?

 

[akimhaneul]

I think I'm still confused why it can't be over 50%. Can anyone help?


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[betterfuture]

This has always confused me, I'm not sure why. I think when I first heard about recombination frequency, I saw the definition as # of recombinant offspring / # total offspring. I thought that if all offspring were recombinant, the frequency would be 1. It sounds like you're defining it in terms of how likely it is for a recombination event to occur?

Yeah. So the percentages are roughly proportional to how far apart the genes are. Here is what I got:

4. Why is the highest possible recombination frequency 50%? The recombination frequency between two genes is equal to the proportion of offspring in which a recombination event occurred between the two genes during meiosis. The recombination frequency between two genes cannot be greater than 50% because random assortment of genes generates 50% recombination (non-linked genes produce 1:1 parental to non-parental. Thus, the recombination frequency would be non-parental/total Æ 1/(1+1) = 50%).

source: http://ocw.mit.edu/courses/biology/...logy-spring-2005/recitations/section16_ak.pdf​