The most important feature that permits a gene to act as a molecular clock is The most important feature that permits a gene to act as a molecular clock is having a reliable average rate of mutation. having a larger proportion of exonic DNA than of intronic DNA. its being acted upon by natural selection. having a large number of base pairs. its recent origin by a gene duplication event

The answer is "The first choice".

Explanation:

The hypothesis of such a molecular clock says because DNA and protein sequences develop at a pace generally constant over time as well as between different organisms. The whole idea is thus incredibly beneficial and for estimation of the historical periods, if the molecular biological hypothesis is valid, then the most significant feature enabling DNA to act as a molecular clock it has a reliable mean mutation.

but there is no

i guess you forgot putting it.