Mutated, the gene I figure (8)
I believe the answer is:
eighteen
'figure' is the definition.
The definition and answer can be both quantities as well as being singular nouns.
Maybe you can see a link between them that I can't see?
'mutated the gene i' is the wordplay.
'mutated' indicates an anagram.
'the'+'gene'+'i'='thegenei'
'thegenei' anagrammed gives 'EIGHTEEN'.
Can you help me to learn more?
(Other definitions for eighteen that I've seen before include "2x9" , "Number of on-field players in an Australian Rules football team" , "Last golf hole number" , "when boy becomes man?" , "age of maturity" .)