Huntington's disease is an inherited condition that affects the nervous system.
The condition is caused by a dominant allele (HHH) of a gene.
The diagram shows the inheritance of the allele in a family.
Complete the table about the family tree.
| Number in the family | |
|---|---|
| Number of males | 4 |
| Number of people who are homozygous recessive for the gene | |
| Number of people who have Huntington's disease |
Person 1 and person 2 are expecting another baby.
Determine the probability that the baby will have Huntington's disease by completing a genetic diagram (Punnett square) for Person 1 and Person 2.
The Huntington's allele (HHH) codes for a mutated protein called huntingtin. Huntingtin protein can damage neurones in the motor cortex, which controls voluntary movements. It can also damage neurones in the cerebral cortex, which is involved in memory and cognitive processing.
Explain why person 2 starts to develop symptoms of Huntington's disease and suggest what these symptoms might be.