Answer: microevolution.
Explanation:
Allele frequencies in a population may change due to gene flow, genetic drift, natural selection and mutation
By binding to DNA it triggers the transcription of a specific gene.
It becomes inactive in the stomach because of the stomach having a MUCH greater PH level then the mouth. It is typically 1.0-2.0 in the Stomach which is extremely acidic which causes it to change shape and therefore inactive.