Question

Could you please explain what it means for a section of DNA to be considered a molecular clock and why neutral mutations are important in this measure of time?

Answer 1

The neutral mutations are a means for providing diversity in organisms. There are 23 amino acids and they are coded for by 256 codons. Sometimes a slight mutation won't cause the amino acid to be changed...rather it will cause another version a the same amino acid to be produced instead e.g. a point mutation at the codon UUU coding for Phenylalanine can lead to UUC, which also codes for Phenylalanine, but over time small mutations such as these bring diversity into the genetic codes of organisms

Answer 2

The sequences of DNA that are used for molecular clocks are generally noncoding sections. That means they don't code for proteins. A segment that doesn't code for protein probably does not affect the fitness of the organism and thus it is not subject to selection.

So, mutations can happen and they won't be selected against. It just so happens that mutations in a particular sequence of DNA tend to occur at a standard rate and that rate will be the same for that same sequence in closely related organisms. So you can compare two related species and you can tell how long ago they diverged from a common ancestor by how many mutations have happened between the two. The clock is set up based on the most recent fossil that would have been ancestral to the two related species you are studying.

Answer 3

Thank you both!