Answers to the MCQs

Autosomal recessive (AR) genes or traits are only expressed in homozygotes for the gene. Horizontal inheritance occurs and affected individuals usually have normal parents. Mating between heterozygotes will produce individuals with a 25 per cent risk of being affected. Both sexes are equally affected, although AR genes may show a sex influence, e.g. haemochromatosis is AR but has a higher incidence in males due to a lower dietary iron intake and menstruation in females. There is an association with consanguinity.