Huntington's disease is a progressive brain disorder caused by a dominant allele.
The pedigree diagram shows the inheritance of Huntington's disease in a family.
HHH represents the dominant allele for Huntington's disease, and hhh represents the recessive allele.
Person P in the family tree must have the genotype Hh\text{Hh}Hh.
Explain how you can tell this from the family tree.
Person P and Person Q are expecting another child.
Complete a genetic diagram to calculate the probability that the child will develop Huntington's disease.
hhHh\begin{array}{c|c|c} & \mathbf{h} & \mathbf{h} \\ \hline \mathbf{H} & \quad & \quad \\ \hline \mathbf{h} & \quad & \quad \end{array}HhhhProbability = ………………………\dots\dots\dots\dots\dots\dots\dots\dots\dots………………………
Scientists have developed a new therapeutic drug that may prevent the onset of Huntington's disease. Before this drug can be approved for general human use, it must be trialed extensively.
Give two reasons why new medicines are tested on cell cultures and animals before they are given to healthy volunteer subjects in human clinical trials.