EK bio 1001 question on frame shift mutations

[ozzi]

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Which of the following DNA Lesions will NOT result in frame shift mutation?

A) 1 missing base pair
B) 2 altered base pairs
C) 3 deleted base pairs
D) 2 inserted base pairs

Can some one plz explain why the answer is B.

 

[ljc]

Which of the following DNA Lesions will NOT result in frame shift mutation?

A) 1 missing base pair
B) 2 altered base pairs
C) 3 deleted base pairs
D) 2 inserted base pairs

Can some one plz explain why the answer is B.

DNA base pairs are read in groups of 3. For instance:

AAA || BBB || CCC || DDD

Each letter corresponds to one "frame," which is read as a single unit. Frame shift means that something is added or subtracted to change those groups of 3:

Added: AAZ || ABB || BCC || CDD
Subtracted: AAB || BBC || CCD || DDX

See how every frame is read "wrong" (relative to the original above) when you add or subtract something? This is because of a frame shift. If you change 2 base pairs, sure those frames may be read wrong, but everything else would be okay:

AXZ || BBB || CCC || DDD

The first frame is wrong, but the other 3 are fine. No frame shift. They start and end at the same spot they did in the original.

Edit: and technically, I think C is correct too, because if the deletions were close enough together, the majority of the molecule would be unaffected. But B is a much better answer.

 

[chiddler]

I agree. C should also be correct in addition to B.

 

[SaintJude]

First I thought that C in addition to B. But then I looked it up on NIH website and it said

"A frameshift mutation is a type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three. "Divisible by three" is important because the cell reads a gene in groups of three bases. "

Now I think it's ONLY C.

Edit: Added this, later..."If you look at the degnerate code, altering 2 bases will always change the amino acid from one to another. But it would not cause a downward frame shift."

 

[chiddler]

First I thought that C in addition to B. But then I looked it up on NIH website and it said

"A frameshift mutation is a type of mutation involving the insertion or deletion of a nucleotide in which the number of deleted base pairs is not divisible by three. "Divisible by three" is important because the cell reads a gene in groups of three bases. "

Now I think it's ONLY C.

yeah but notice B is not insertion or deletion. just alteration.

 

[SaintJude]

Ok, then this is just one of those flawed EK questions where you get the "gist" and move on. Yeah, it's B & C!

At least I refreshed my mind: Frame mutations are caused by additions or deletions of DNA bases that are not divisible by the number three.

 

[ozzi]

So what you guys are saying is that B and C can be right? Thanks

 

[chiddler]

yup yup.

B: two alterations. One amino acid may change, but the reading frame is unaltered.

C: Three deleted base pairs...WAIT. These are not necessary adjacent! What if bp#10, #199, and #212 are deleted? That will cause a frame shift at all base pairs prior to the last deletion!

SO! B is a better answer if i'm not mistaken! Then again, what does the term "lesion" indicate?

 

[ljc]

Yea, B is definitely the better answer. Though if B weren't there or were something else (such as "Insertion of 1 base pair"), C would be correct also.

 

[Temperature101]

Which of the following DNA Lesions will NOT result in frame shift mutation?

A) 1 missing base pair
B) 2 altered base pairs
C) 3 deleted base pairs
D) 2 inserted base pairs

Can some one plz explain why the answer is B.

B is the only answer...C is definitely wrong because they did not say if the three deleted base pairs are next to each other. If they had said that, C would be a good answer as well. But you are assuming that these base pairs are next to each other, which was not said in the question stem.

Edit...Someone above my post said the same thing...Me too late.