State one reason why a doctor might advise genetic testing for a mutation in the gene $\textit{BRCA1}$ and explain why this mutation would increase the person's risk of breast cancer.
DNA sequencing is one way of checking for mutations in $\textit{BRCA1}$. Before sequencing, the DNA sample is first put through the polymerase chain reaction (PCR). Suggest why PCR is used when testing for mutations in $\textit{BRCA1}$.
Genetic screening has shown that in the UK: • $1$ in $400$ females carry a mutated allele of $\textit{BRCA1}$ • $70\%$ of females with a mutated allele of $\textit{BRCA1}$ will develop breast cancer by the time they reach $80$ years old. In 2022, the female population of the UK was $3.5 \times 10^7$. Calculate the number of females in the UK population in 2022 who are estimated to develop breast cancer by the age of $80$ years old. Give your answer in standard form. Show your working.
One advantage of genetic screening is to find which drugs should be chosen for cancer treatment. A study was carried out on women with breast cancer who had been treated with a DNA-damaging drug that kills tumour cells. All of the women had been tested for $\textit{BRCA1}$ mutations. One group had a $\textit{BRCA1}$ mutation and the other group did not have a $\textit{BRCA1}$ mutation. The researchers used data to assess the probability of survival for the women in each group after treatment with the drug. Fig. 5.1 shows the probability of survival over a time period of up to $180$ months. The researchers proposed the hypothesis that the DNA-damaging drug is more effective in women with a $\textit{BRCA1}$ mutation. Discuss whether the results in Fig. 5.1 support the hypothesis put forward by the researchers.