Chapter 17, Problem 22A

Summary Introduction

To write:

Method of use of molecular clocks when all mutations do not occur at the same rate and whether they can be used as reliable evidence of phylogeny.

Introduction:

The concept of molecular clocks was developed by Linus Pauling and Emile Zuckerlandl.

Explanation of Solution

The molecular clock refers to a term for a technique which uses the rate of mutation to determine the time in prehistory when two or more life forms may have diverged from each other.

The data used for such calculations are nucleotide sequences of DNA, RNA or amino acid sequences in proteins.

The molecular clock uses a particular gene which has a definite, predetermined rate of mutation. Thus, such genes may be used to determine the evolutionary pattern.

According to biologist Motto Kimura’s neutral theory of mutations, most of the mutations occurring do not have an effect on the evolutionary patterns. Such mutations may be fixed and natural selection may or may not favour them.

Thus, ‘relaxed molecular clocks’ were developed which allow the variation of molecular rates among lineages.

Molecular clocks may be used as reliable sources of phylogeny in the future with a little advancement in studies. In the future, studies should aim to throw light on the variation of genomic molecular clocks to understand them better.

Conclusion

Molecular clocks have been used to investigate several forms of information like the origin of modern humans and the date of the divergence of humans and chimpanzees.