Huntington's disease is a neurodegenerative disorder that progressively damages nerve cells in the brain. It causes coordination, cognitive, and psychiatric issues, with symptoms most commonly appearing when a person is between 30 and 50 years of age.
The disease is inherited and is caused by a dominant allele (HHH) and not the recessive allele (hhh).
A homozygous recessive male mates with a heterozygous female.
Use a genetic diagram to show the parental genotypes, the gametes produced, and the possible genotypes and phenotypes of the offspring.
Explain why it is difficult for a doctor to decide if an asymptomatic 20-year-old has the condition based solely on physical symptoms.
Suggest what other information or methods the doctor could use to determine if the 20-year-old will develop the disease.
Many other genetic disorders, such as cystic fibrosis, are caused by recessive alleles rather than dominant alleles.
Explain how examining a family pedigree diagram would enable you to determine if a condition is caused by a recessive allele.
