Gentamicin is an antibiotic used to treat severe bacterial infections in children. (a) Some children have a genetic mutation in the gene MT-RNR1. If gentamicin is given to children with this genetic mutation, it can cause deafness. Before gentamicin can be given to a child with a severe bacterial infection, PCR (polymerase chain reaction) and electrophoresis are used to test whether the child has this mutation. If the mutation is found, a different antibiotic must be given. (ii) PCR with primers specific to the MT-RNR1 gene is used to amplify DNA from the child that is being tested. The PCR primers are designed so that the amplified product of the normal allele of MT-RNR1 is longer than the amplified product of the mutant allele. Gel electrophoresis is used to separate the PCR products. Fig. 3.1 shows the results of gel electrophoresis after using this method of PCR on DNA samples collected from three children. [Figure 3.1]