Final answer:
Huntington's disease is caused by a mutation in the gene on chromosome 4, resulting in neurodegeneration with symptoms typically starting around age 40. The symptoms progress and do not subside with age, and it has a dominant inheritance pattern, giving a 50% chance of being passed to offspring.
Step-by-step explanation:
Huntington's disease is an inherited neurodegenerative disorder that usually begins to show symptoms in middle age. It is caused by a mutation in the gene that produces the huntington protein, leading to the production of an abnormal protein with a longer sequence of glutamine residues. This genetic mutation does not reside on the 26th chromosome, as humans only have 23 pairs of chromosomes (46 total), but rather, it is the result of a defective gene on the chromosome 4. The symptoms of Huntington's disease do not subside by age 35 to 40; instead, they progress over time, leading to serious physical and cognitive decline until the eventual death of the patient.
Huntington's disease symptoms are not the opposite of Parkinson's disease; rather, they include involuntary spastic movements and cognitive issues, which differ from the tremors, slowed movement, and rigidity characteristic of Parkinson's disease. The onset of symptoms typically does not occur until around age 40, which means individuals may have already passed the mutation to their offspring. A person who inherits the Huntington allele has a 50% chance of developing the disease due to its dominant inheritance pattern.