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Topic: Mutations: math question  (Read 6879 times)

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Offline spirochete

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Mutations: math question
« on: March 24, 2008, 08:29:19 PM »
How many times should you expect to find a six base pair DNA sequence in a 11,000 BP fragment of DNA?

I am 90% lost on how to do this.  I feel like part of the answer should involve raising 0.25 to the sixth power, because that's the probability of finding a paticular sequence in six nucleotides.

Offline Martingale

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Re: Mutations: math question
« Reply #1 on: March 24, 2008, 10:10:41 PM »
How many times should you expect to find a six base pair DNA sequence in a 11,000 BP fragment of DNA?

I am 90% lost on how to do this.  I feel like part of the answer should involve raising 0.25 to the sixth power, because that's the probability of finding a paticular sequence in six nucleotides.

1) Are A-T / T-A and G-C /C-G equally likely in a DNA molecule?

2) Are you allowing for overlaps?

If you allow for overlapping then the particular sequence you are looking for will have an effect on the expected value.
Professor: Anywho, your net suits will let you experience Fry's worm-infested bowels as if you were actually wriggling through them.
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Offline spirochete

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Re: Mutations: math question
« Reply #2 on: March 25, 2008, 04:24:03 PM »
I believe we can assume that AT/CG are equally likely, and I'm not sure if we're allowing for overlaps.  I think this is how the problem was supposed to be solved:

(O.25^6)(11,000) 

I'm not sure if this method accounts for overlaps.  It seems like it does.

Offline Martingale

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Re: Mutations: math question
« Reply #3 on: March 25, 2008, 05:45:18 PM »
I believe we can assume that AT/CG are equally likely, and I'm not sure if we're allowing for overlaps.  I think this is how the problem was supposed to be solved:

(O.25^6)(11,000) 

I'm not sure if this method accounts for overlaps.  It seems like it does.

It does but it ignores the dependence between the overlaps
Professor: Anywho, your net suits will let you experience Fry's worm-infested bowels as if you were actually wriggling through them.
Dr. Zoidberg: There's no part of that sentence I didn't like.

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