Introns and splicing - 30' in class exam EK

[pm1]

The intron sequences of identical genes in closely related species are often very different. Which of the following is most strongly suggested by this evidence?
A. Identical genes in closely related species may code for different proteins.
B. Changes in amino acid sequence of a protein do not necessarily change protein function.
C. Intron sequences are heavily characterized by selective pressure.
D. Selective pressure has little or no role in the development of intron sequences.

Answer: D

Can somebody please explain why is A wrong?
Thanks!

---

Members don't see this ad.

 

[chiddler]

"Identical genes in closely related species may code for different proteins. "

if they are identical, the proteins cannot be different, right?

 

[pm1]

"Identical genes in closely related species may code for different proteins. "

if they are identical, the proteins cannot be different, right?

seems pretty obvious...

but can't a specific gene go through different splicing? or is the intron and exon areas a constant in a gene?

 

[MedPR]

seems pretty obvious...

but can't a specific gene go through different splicing? or is the intron and exon areas a constant in a gene?

Only the introns get spliced out; they are worthless. That's why D is the answer. Introns don't matter.

 

[pm1]

Only the introns get spliced out; they are worthless. That's why D is the answer. Introns don't matter.

okay.
I guess I was confused from a statement I ran into an earlier passage saying:

Different patterns of splicing can produce different
protein from the same primary RNA transcript. The splicing reaction is remarkably
precise.

so I was under the impression that splicing could vary. But that is not the case right? An intron is always going to be an intron, and it will be always spliced out. (right?)

and in regards to the quote, how is it not contradictory to the answer of the OP question?

 

[MedPR]

Iirc the introns are always spliced out, but different proteins can arise from identical pre-mRNA sequences because the exons can be joined in different sequences.

So I could have a pre-mRNA sequence of 1-intron-2-3-4-5-intron-6-7.

Splice out the introns and now I could have 1-2-3-4-5-6-7, or I could have 1-3-2-4-5-6-7, or any combination of those exons.

 

[pm1]

Iirc the introns are always spliced out, but different proteins can arise from identical pre-mRNA sequences because the exons can be joined in different sequences.

So I could have a pre-mRNA sequence of 1-intron-2-3-4-5-intron-6-7.

Splice out the introns and now I could have 1-2-3-4-5-6-7, or I could have 1-3-2-4-5-6-7, or any combination of those exons.

ahn.. that makes perfect sense!
Thank you!

 

[milski]

Iirc the introns are always spliced out, but different proteins can arise from identical pre-mRNA sequences because the exons can be joined in different sequences.

So I could have a pre-mRNA sequence of 1-intron-2-3-4-5-intron-6-7.

Splice out the introns and now I could have 1-2-3-4-5-6-7, or I could have 1-3-2-4-5-6-7, or any combination of those exons.

It has been a while but I think the only possibilities are 1-2-3-4-5 or 1-6-7 or 1-2-3-4-5-6-7. I think that rearrangement of the order of exons does not happen. But I might be very, very wrong.

 

[Kennedypjp]

Good thinking..

 

[Morsetlis]

The intron sequences of identical genes in closely related species are often very different. Which of the following is most strongly suggested by this evidence?
A. Identical genes in closely related species may code for different proteins.
B. Changes in amino acid sequence of a protein do not necessarily change protein function.
C. Intron sequences are heavily characterized by selective pressure.
D. Selective pressure has little or no role in the development of intron sequences.

Answer: D

Can somebody please explain why is A wrong?
Thanks!

Closely related species have similar selective pressures. Therefore, their encoded proteins should be similar. Encoded proteins come from exons. If introns of similar proteins are different, then the introns do not care about selective pressure.

A is a true statement, but the evidence involves introns. The question says nothing about exons, or promoters, or epigenetics, or regulation which will affect how the protein is expressed.
B, likewise, does not address the introns, which is the whole point of the question.
C is proven false by the species being closely related, and the introns ARE different.

 

[Morsetlis]

It has been a while but I think the only possibilities are 1-2-3-4-5 or 1-6-7 or 1-2-3-4-5-6-7. I think that rearrangement of the order of exons does not happen. But I might be very, very wrong.

My Immunology professor would be devastated.