# genetics question

Discussion in 'MCAT: Medical College Admissions Test' started by pezzang, May 7, 2007.

1. ### pezzang Senior Member 10+ Year Member

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Does anybody know how to find GC frequency? I have looked up online but couldn't find it. Do you count GC portion only or G and C separately?

2. ### bluesTank Zombie 5+ Year Member

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I've never heard of finding a "GC Frequency"

Is that some property inherent to a certain species?

I guess if you had a strand, you would count the G-C pairs, and the frequency would be (G-C pairs) / (total pairs)

3. ### mongrel Assoc. Prof. Dogsuit 5+ Year Member

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I think bluesTank is correct with his math. Another way to answer the question is how to find relative GC frequency from a lab experiment. This could be done by measuring the 260 nm absorbance of your dsDNA sample as you increase the temperature. Once you get to the "melting temperature" where your double-strand becomes two single-strands (and absorbance increases), you can compare it to another sample with a known GC freq. Melting temp should increase as GC freq increases due to more hydrogen bonds between the two strands.

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4. ### DocInProgress 7+ Year Member

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I think the GC frequency is beyond the scope of the MCATs as I have never encountered that term in the Kaplan and the EK books.

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So A=T is two H-bonds between them. G C pair has 3 H-bonds...

6. ### CATallergy 2+ Year Member

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my guess: every bond between the 2 DNA strands is either GC or AT. for example, you might say that some promoter sequence has a high AT frequency. in your example, 11 out of the 16 nucleotides are G or C (and h-bond to C and G, resp. & not shown). 11/16 = about 70%

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