Individuals with Huntington's disease possess an allele that causes severe symptoms by

a. replacing pairs of chromosomes.

b. halting the process of gene expression.

c. producing certain abnormal proteins.

d. regulating the sequences of nucleotides.

C) Producing certain abnormal protiens

Explanation:

Mutations in HTT gene causes Huntington disease. The HTT gene provides instructions for making a protien called huntingin. This protien plays an important role in the neurons of brain. Thus as the gene coding for this protien is mutated, abnormal protien is synthesized.