Most nonsense mutations in genes that encode structural proteins cause a null ("knockout") phenotype.

How many "sense" codons can be converted into nonsense codons (TAA, TAG, TGA) by single base pair substitution mutations?

TGA (opal)

Answer:

Explained below

Explanation:

A mutation in a gene that results in total loss of the normal function of the gene product encoded by that gene, resulting in a Null phenotype.

Changes in DNA sequence are termed as nonsense mutation that introduce a stop codon, resulting in a non functional protein. This terminology results stop codons have also worked as nonsense codons.

There are three different stop codon-

In RNA

UAG (amber) UAA (ochre) UGA (opal)

In DNA

TAG (amber) TAA (ochre) TGA (opal)