EK Bio in class exam #2, question 33

[slz1900]

The question basically says:

Intron sequences of identical genes in related species are often different. What is most strongly suggested by this?

A. Identical genes may code for different proteins
B. Changes in amino acid sequence don't affect protein function
C. Intron sequences are characterized by selective pressure.
D. Selective pressure has little or no role in the development of intron sequences.

EK says the answer is D, but I don't see why A couldn't be right as well. If pre mRNA is being spliced differently, it seems fair to assume that the proteins made will be different

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[image187]

The question basically says:

Intron sequences of identical genes in related species are often different. What is most strongly suggested by this?

A. Identical genes may code for different proteins
B. Changes in amino acid sequence don't affect protein function
C. Intron sequences are characterized by selective pressure.
D. Selective pressure has little or no role in the development of intron sequences.

EK says the answer is D, but I don't see why A couldn't be right as well. If pre mRNA is being spliced differently, it seems fair to assume that the proteins made will be different

Remember that if a gene takes a mutation to an intron, nothing will happen to the resultant protein assuming the splice sites are intact. I think the point of the question is that the makeup of the introns can be governed by random mutations with no effect on the function of the organism, while the sequence of exons is more determined by natural selective pressures because they actually play a direct role in protein structure. The pre-mRNA wouldnt be splicediet different sites in this situation so the resultant proteins in these two species would be essentially the same

 

[slz1900]

Remember that if a gene takes a mutation to an intron, nothing will happen to the resultant protein assuming the splice sites are intact. I think the point of the question is that the makeup of the introns can be governed by random mutations with no effect on the function of the organism, while the sequence of exons is more determined by natural selective pressures because they actually play a direct role in protein structure. The pre-mRNA wouldnt be splicediet different sites in this situation so the resultant proteins in these two species would be essentially the same

Gotcha. I didn't interpret the question as saying that the introns had the same splice sites but a different nucleotide sequence, but instead that the actual introns were different, ie the pre mrna was spliced differently. Man I hate how ambiguous some of these EK questions are.