Many oncogenes result from mutations that cause a protein to be expressed in cells where it is normally not expressed or at inappropriate times during development. This type of mutation can be described as

The correct answer is: Gain-of-function mutation.

Explanation:

Mutation can be defined as the sudden alteration in the sequence of DNA or Deoxyribonucleic Acid, which if happens in the protein-coding region of the gene can cause the protein to become non-functional or can change the function of the protein. If such a mutation happens in the untranslated region or the regulatory sequence of the gene, it can cause: the gene to get constitutively (all the time) expressed at high levels, such that its expression can no longer be regulated or controlled. This type of mutation is called a Gain-of-function mutation. the expression of the gene to get repressed or suppressed, such that very less amount of protein or no protein that is encoded by the gene is produced. This type of mutation is called a Loss-of-function mutation.