A researcher is interested in testing the role for a highly- conserved amino acid in the function of a mouse protein. She has been unable to locate any pre- existing variants in this codon among a large number of available mouse strains. What might be her approach to generating such mutants?

A) Use RNAi to knockdown the expression of the target gene.
B) Use RNAi to interfere with translation of the gene.
C) Use transposons to generate insertion alleles in the gene.
D) Measure the expression of this gene in mice as they develop.
E) Use CRISPR- cas to cause DNA cleavage at the codon encoding this amino acid.