Down's syndrome is caused by

  1. a gene mutation in haemoglobin
  2. an extra chromosome 21, giving 47 chromosomes
  3. a missing X chromosome
  4. a virus
Answer

B) an extra chromosome 21, giving 47 chromosomes

A chromosome mutation. O Level Biology · Topic 17 Inheritance · 17.3 Inheritance

Biology MCQ · More O Level Biology: Inheritance MCQs · Practise