(a) Heritable changes in the sequence of DNA bases that produce an observable phenotype
(b) Heritable changes in the sequence of DNA bases
(c) Mistakes in the incorporation of amino acids into proteins
(d) Heritable changes in the mRNA of an organism
Mutations are sudden changes that takes place in DNA sequence of an organism. These are the permanent changes that can be either induced or occur naturally leading to variations. At the level of DNA, these are changes in sequence of DNA bases due to substitution, insertion or deletion of amino acids.