Pendred syndrome is a rare genetic disorder.
People with Pendred syndrome suffer from bilateral sensorineural hearing loss (caused by developmental defects in the cochlea of the inner ear, which detects sound waves) and thyroid dysfunction, often leading to a goitre (a physical enlargement of the thyroid gland in the neck).
The inheritance of Pendred syndrome in a family is described below:
A scientist makes this statement: "The allele causing Pendred syndrome in this family is recessive."
Explain why this statement is correct. Use evidence from the family pedigree.
Person A and person B are expecting another baby. Determine the probability that the baby will have Pendred syndrome by considering their genotypes. Use PPP for the dominant allele and ppp for the recessive allele.
Person C finds it extremely difficult to follow a spoken conversation in a crowded, noisy room and frequently experiences physical discomfort when swallowing dry food.
Explain why this is, using your knowledge of the symptoms of Pendred syndrome.
97 exam-style questions on OCR GCSE Biology 5.1 Inheritance, covering 5.1.1 The genome, 5.1.2 Environment and phenotype, 5.1.3 Variants and mutations, 5.1.4 How genetic variants influence phenotype, 5.1.5 Asexual and sexual reproduction, 5.1.6 Haploid and diploid, 5.1.7 Meiotic cell division, 5.1.8 Single gene inheritance, 5.1.9 Predicting single gene crosses, 5.1.10 Sex determination, 5.1.11 Multiple gene inheritance, and 5.1.12 Development of our understanding of genetics. Each one has a worked solution and a mark scheme showing where the marks go.