Southern Blotting

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Southern Blotting

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sfk
Forum Elite

Topics: 43
Posts: 294

10/16/07 - 10:06 PM

After amplification of exon 9 of the LDL receptor gene using PCR, a scientist employs RFLP analysis with Southern blotting to identify a point mutation in codon 408. This mutation has resulted in the missense mutation of GTG (Val) to GTA (Met):

Normal: CTGGTGCAA
Mutant: CTGGTACAA
Exon 9: 222 bp

NlaIII is a restriction enzyme recognizing the short palindrome GTAC, which is not present in the normal exon 9.

The researcher digests the amplified exon 9 with this enzyme, then subjects it to Southern blotting with a probe directed against the entire amplified region. Which of the following banding patterns would most likely be found in an individual heterozygous for the mutation described?

A. One thick band of 222 bp
B. Three bands of 180, 32 and 10 bp
C. Three bands of 222, 126 and 96 bp
D. Two thick bands of 126 and 96 bp
E. Two bands of 444 and 222 bp

Edited by new_n_lost on 10/18/07 - 01:13 PM. Reason: Edited the font

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drgho
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Topics: 1
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10/17/07 - 02:40 AM

C. three bands 222, 126 & 96 bp.

sfk
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Topics: 43
Posts: 294

10/18/07 - 11:35 AM

Awesome!!! as usual u r right, dr-genetics-gho grin

could u pls help me on this

http://www.prep4usmle.com/forum/thread/61491

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drgho
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10/19/07 - 10:20 AM

sfk wrote:
Awesome!!! as usual u r right, dr-genetics-gho grin

could u pls help me on this

http://www.prep4usmle.com/forum/thread/61491

No. I am not good at genetics....just lucky.

I am not sure how LOD score will be asked. The idea of LOD score is to troubleshoot the error in recombination frequency...but no idea how to deduce the LOD score from cM.

sureshrx
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10/20/07 - 12:09 PM

could you pl explain the answer?

drgho
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Topics: 1
Posts: 115

10/24/07 - 02:00 AM

The restriction enzyme cuts the mutant gene but not the normal gene. So, the hetergenous subject will have one band for the whole exon 222 bp and two bands for cut mutant exon in which the sum of those two bands is 222bp. So only C fits. the others not.

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