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Jun 18, 2002
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Here is a multiple choice for you:

Which of the following is NOT a type of genetic mutation?

A. point
B. silent
C. Insertion
D. frameshift
E. None of the above are types of genetic mutations

Answer: (according to Kaplan subject test answer key)
"E is correct. Point mutations occur when a single nucleotide base is substituted by another. A silent mutation is a point mutation that occurs in a noncoding region, or it does not change the amino acid sequence due to the degeneracy of the genetic code. A frameshift mutation is either an insertion or deletion of a number of nucleotides. These mutations have serious effects on the protien coded for, since nucleotides are read as series of triplets. The addition or loss of nucleotides (except in multiples of 3) will change the reading frame of mRNA."

Okay, all of that is TRUE, but E does not sound like a right answer. I read this question about 15 times trying to see if I was just reading it wrong. I got an 'A' in molecular biology, and I think I know genetics inside and out, but this was just screwing with me. Is it possible that there is just a messed up question on this test? And if so, why did I choke up a thousand dollars for this Kaplan DAT stuff?

ONE other thing for those of you who may have taken the DAT already. I've run into two different questions on the practice tests asking essentially the same thing, and each one had a different answer. Here it goes...

"Red is dominant to white in a certain flower. To test whether a red offspring is heterzygous or homozygous in this flower...

A. cross it with a red plant that had a white parent
B. cross it with a red plant that had two red parents
C. cross it with a white plant
D. Two of the above will work
E. None of the above will work

The answer according to Kaplan is C, but in a VERY simillar question on another test, they said the answer could be D. If you have a known heterozygous organism and you cross it with an unknown, you can STILL figure out the genotype, isn't that right? If the unknown is homozygous Dominant (and you crossed it with the KNOWN heterozygote), all the offspring would still be dominent phenotypically, and if the unknown were heterozygous, 1/4 of the offspring would express the recessive trait. What would you predict the actual DAT would accept as the right answer?

Okay that's all for now. Expect more questions later this week.


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For your first question, I encountered the same one....

Point mutation is where one of the nucleotide sequence is substituted by another. Lets say, GAU to GAC, something like that, most of times, if the 3rd nucleotide's substituted, nothing will hapeen because they still translated to the same amino acid, in this case will be the mutation is SILENT. Keep in mind that they ask for GENETIC MUTATION, so even though no physical mutation occur, but the gene still mutated.

It's a bad question, don't worry about it.

as for the second one......i agree with you on D.

what am i going to put on the test? i will probably toss a coin or something...


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Jun 24, 2002
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Hey Portlander,

I used Kaplan guides, Barron's, Shaums and Topscore. There are errors and bad questions in all of them. I remember how frustrating it was to spend 1/2 hour going back and trying to figure out why what I thought was right is wrong according to their answer keys. It's kind of a bad approach.... don't worry about getting the right answer in the bio section. Just know the diff. bwn the types of mutations...know the concepts. Nothing in the DAT will be as challenging, trust me. It's worse when that happens in the chemistry section because it can be a math error on their part.

Anyways, for your 2nd question, I'd say D is correct.

C is correct because that's a standard test cross...you're crossing it with a homozygous recessive.
B is incorrect because a red plant with 2 red parents can be either RR or Rr (if R=red and r=white). That really complicates the crosses.
A is correct because a red plant with one white parent can only be Rr and if you cross this with your mystery red (either Rr or RR), you're getting different results in the punnet square: either 4 reds making it a homozygous dominant or 3 reds:1 white, making it heterozygous.
:confused: I know that's not very clear but since you took genetics I'm sure you already know this.
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