Question

(HELP) A geneticist was able to reconstruct a sequence of mitochondrial DNA of a prehistoric insect that was encased in amber. A segment of this DNA was found to have the sequence AGGTCCTAAG. This segment of DNA has had a single mutation every 100 million years. The following sequences have mutated from the original prehistoric sequence, as shown by the highlighted substituted nucleotides. Which of these sequences most likely belongs to this insect's descendant after 200 million years have passed?

Answer 1

Hmm can you give a bit of info about the "following sequences"?

My guess right now would be to go with the one with two highlights - 200 million years have passed, so we can deduce two mutations have accrued. But, given the answer choices, the problem may turn out to have a twist or something.

Answer 2

Well these are the answer choices

AAGTTTCAGG
AAGTTTTAAA
AGATCTCGGA
AGGCCCCAAG

Answer 3

I would go with the fourth one - two of the nucleotides, relative to the original, have been substituted - indicating that two hundred million years have passed. Does that make sense?

Answer 4

I was between c and D but im guessing im going with the 4th one too. thanks !

Answer 5

@kma230 is correct as usual - I would just like to note that in real life it is not that simple. The answer probably is D.

Sometimes to mutations occur in the same location. If the initial nucleotide was a C and it changed to an A, then to a T, then you would only count one mutation instead of two. This would cause you to underestimate the time since the organisms diverged.

Similarly, if the initial nucleotide was a C, it mutated to an A and then mutated back to a C, it would look as though no mutation occurred at all! Then you would really drastically underestimate the time since divergence, since the sequences are apparently the same!

If this method is applied to two currently living species and comparison of sequence of DNA is used to calculate how long ago the organisms diverged, then you also have to take into account the probability that the same mutation occurs at the same site and makes it appear that the organisms are more closely related than they actually are.

Sorry all, but it annoys me when this method is presented as giving an absolute and correct answer. It does not. What it actually gives you the lower bound, the least possible time, since the organisms diverged.

Answer 6

haha its true and thanks !