Final answer:
The increased severity of Huntington's disease across generations is explained by Genetic anticipation, a process where a disorder's severity or earlier onset increases in each generation. Huntington's is a dominant autosomal disorder with a 50 percent inheritance chance.
Step-by-step explanation:
The increase in the severity of Huntington's disease from generation to generation within a family, as characterized by an earlier age of onset and reduced time to death, can best be explained by Genetic anticipation. This phenomenon occurs when a genetic disorder becomes more severe or has an earlier onset with each generation. In the case of Huntington's disease, the condition is caused by the expansion of CAG trinucleotide repeats in the HTT gene, which tends to increase in number with each generation, thereby increasing the severity of the phenotypic expression of the disease.
Huntington's disease is a dominant autosomal disorder, which means it only requires one copy of the defective gene to manifest symptoms. It is characterized by the degeneration of nerve cells in the brain, leading to physical, psychological, and cognitive symptoms that typically do not become apparent until middle age. The condition is inherited from a parent with a 50 percent chance of passing the mutation to each offspring. Affected individuals are heterozygous for the Huntington allele, with one normal allele and one defective allele (Hh).