Huntington's disease is a genetic condition that causes the progressive breakdown of nerve cells in the brain.
The condition is caused by a dominant allele.
Explain what is meant by the term dominant allele.
Symptoms of Huntington's disease usually do not become apparent until the person is between 30 and 50 years of age. Suggest why this late development of symptoms makes it difficult to reduce the number of people born with the condition.
A woman who is heterozygous for Huntington's disease has a child with a man who is also heterozygous.
Use a genetic diagram to show the genotypes of these parents, the gametes they produce, and the genotypes and phenotypes of any possible offspring.
Use the letter HHH for the dominant allele and hhh for the recessive allele.
Explain what is meant by the term mutation.
