Final answer:
Genetic anticipation in paternal transmission of Huntington's Disease (HD) is caused by the expansion of trinucleotide repeats in the huntingtin gene, resulting in earlier onset and more severe symptoms in subsequent generations.
Step-by-step explanation:
Genetic anticipation in paternal transmission of Huntington's Disease (HD) is due to the expansion of trinucleotide repeats in the huntingtin gene. In the case of HD, the number of CAG repeats increases with each generation. This phenomenon results in earlier onset and more severe symptoms of the disease in subsequent generations. The expanded repeat disrupts the normal functioning of the huntingtin protein, leading to the degeneration of neurons in the brain.