Anonsense mutation in a gene a nonsense mutation in a gene has no effect on the amino acid sequence of the encoded protein alters the reading frame of the mrna changes an amino acid in the encoded protein introduces a premature stop codon into the mrna

introduces a premature stop codon into the mRNA

Explanation:

A nonsense mutation is a mutation in which an amino acid–specifying codon is changed into a termination codon or stop codon. A stop codon is a codon that does not code for any amino acid and serves to terminate the process of protein synthesis as ribosomes encounter it on the mRNA.

There are three stop codons: UAA, UAG, UGA. A nonsense mutation introduces a stop codon in place of an amino acid encoding codon. It results in the formation of truncated protein which is shorter than the normal protein. Truncated proteins are mostly nonfunctional.

i think the miocene epoch spans the time from 23 million to 12 million years ago.