A team of scientists is studying a mitochondrial DNA sequence shared by two species, and they determine that the DNA has a constant mutation rate. The DNA sequences of the two species are shown below.

Species A: GTAGGCATTCGAT
Species B: GCACGCATACGTT

The scientists use the idea of molecular clocks to determine that the two species diverged from a common ancestor 40 million years ago. Based on this information, how much more time would it take for the two species to differ by a total of 10 base pairs?

Can someone please explain it to me, I am having a hard time understanding t

Question

A team of scientists is studying a mitochondrial DNA sequence shared by two species, and they determine that the DNA has a constant mutation rate. The DNA sequences of the two species are shown below. 
  
Species A: GTAGGCATTCGAT 
Species B: GCACGCATACGTT 
  
The scientists use the idea of molecular clocks to determine that the two species diverged from a common ancestor 40 million years ago. Based on this information, how much more time would it take for the two species to differ by a total of 10 base pairs? 

Can someone please explain it to me, I am having a hard time understanding t

blues · Answer

Absolutely.

Imagine that you are living 40 million years ago. You are looking at a certain segment of mitochondrial DNA from an organism which lived then but is extinct now. It has a certain sequence.

Now imagine that you are living today. You are looking at the same mitochondrial DNA from two different organisms which evolved from the organism you looked at 40 million years ago. Both organisms today have acquired some mutations in the DNA, so the sequences are similar but not exactly the same.

By looking at how similar / different the sequences are, you can estimate how long ago the two species shared a common ancestor. If not many mutations have accumulated, the species didn't diverge that long ago - they are closely related. If many mutations have accumulated, they diverged a long time ago.

Is that clearer?

please · Answer

Yeah, I understand that but I don't know how to solve the question..

blues · Answer

OK. So you solve the question by comparing the two sequences. The first thing to do is count the bases which are different in each.

blues · Answer

I count 4, but you should check that as I could *easily* have made a mistake.

blues · Answer

Are you still with me??

please · Answer

YEEAHH! Um, i counted 4 too.

blues · Answer

So now you know that 4 mutations have occurred in 40 million years. From that, you can calculate that one mutation occurs every 10 million years.

The question asks how long time it will take for 10 mutations to occur...

please · Answer

Which would be 10 million years right?

blues · Answer

Hmm. There is 1 mutation every 10 million years. After 20 million years, there are two mutations. After 30 million years, there are 3 mutations.... The question asks, how long will it take for there to be 10 mutations?

please · Answer

I meant 100!!! Sorry.

blues · Answer

No prob. It will definitely take 100 million years for 10 mutations to happen.

The question is a little tricky here with the language. It tells you that 40 million years have already gone by and it asks you how many more will go by to reach 100 million. So the actual answer is 60 million years.

please · Answer

Thats what was confusing me! Thank you so much though!

blues · Answer

Thanks for working through it instead of just asking for an answer. Not everyone does. :D

please · Answer

I noticed! LOL, I just actually want to learn from this! (:

please · Answer

And can you explain annother question for me?