During DNA replication occasional errors can occur resulting in a change in a nucleotide base, for example instead of adding a T, a C is added. If this is not corrected by mismatch repair or other mechanisms, this change represents a

MUTATION

Explanation:

As said in the question, changes in nucleotide bases that make up the genetic material (DNA) occur from time to time. This change called MUTATION can either occur as a result of copying mistakes during replication or be induced by mutagens (mutation-causing components). If the affected cell is not internally corrected using mismatch pair mechanism and it keeps dividing, it could possibly serious problems to the affected organism.

The kind of change described in the question is a SUBSTITUTION MUTATION, in which a nuceleotide base replaces another in the DNA sequence i.e. C replaces T.

i think the answer would be a dominant trait.

parasites can detrimentally affect their host, but also must not allow their host to die before they can complete their life cycle. some parasites have complex life cycles with many different hosts, and have had to find ways of persisting in many different environments during the change from one host to another. ectoparasites live outside the body of the host, and can more easily  disperse, but are  more exposed to predators, parasites, parasitoids. endoparasites live inside the body of the host, and are therefore protected from the outside environment. but they can be  attacked by the host's immune system. they have therefore developed  mechanisms for dispersal such as  complex life cycles.