Huntington disease can strike at an earlier age and bring about a more rapid degeneration and death in successive generations within a family. This phenomenon can be explained by which mechanism?
a. Presence of a transposable element in the gene.
b. Chronic exposure to mutagens in the environment.
c. Expansion of a trinucleotide repeat in the coding sequence of the gene.
d. Presence of an extra chromosome in the germ line.
e. Absence of a gene product that is involved in DNA repair.