How do you calculate the following mutation rates?

Question

Hemoglobin Molecule. ..
Species: Mouse
Different amino acids: 25
Years from common ancestor: 80 Million

Other information: 146 Amino acids in a hemoglobin molecule.

Answer 1

Well, if 25 mutations are occurring in 80 million years, that's about 3.2 million years per mutation. It bears mention that's not an iron-clad figure because it ignores the possibility of several mutations occuring to the same site and it ignores the vast number of mutations which might occur in hemoglobin which are simply unsurvivable. So it might be better to say something along the lines of at least 3.2 million years per survivable mutation.

Of course, that's a bit disingenuous too, because it's going at the problem backwards. Usually what scientists do is take a known mutation rate and compare it to the number of differences to get a time. So presumably that's how they originally knew the divergence time was 80 million years ago - hopefully by comparing the number of differences to something close to the rate we calculated above.

That rate is different for different types of DNA and for different species. Hemoglobin is REALLY important, so it's not tolerant to bad variations which show up and are killed (as I pointed out above). On the other hand, there are non-coding junk sections (like the section they use for paternity tests) which retain just about every mutation that occurs and are highly varied. And a species with a generation time of two minutes is going to have more DNA stress than one with a generation time of 40 years! All this is good - you can use calculations from one stretch of DNA to check your calculations from another stretch and get pretty good estimates.

Anyway, hope that all helps!