Which characteristic in man is NOT inherited?

Analyze the question: We need the condition that is not passed from parents to children through genes.

Explain the concept: Inherited (genetic) traits are controlled by genes on chromosomes. Some come from recessive alleles, some are sex-linked, and others are caused by abnormal haemoglobin genes. Non-inherited conditions are usually caused by environmental factors such as diet or infection.

Go through the options:

• A. Albinism: Inherited. It is an autosomal recessive condition in which melanin is not produced.
• B. Colour blindness: Inherited. It is a sex-linked recessive trait carried on the X chromosome.
• C. Haemophilia: Inherited. It is also a sex-linked recessive trait on the X chromosome, and it causes failure of blood to clot.
• D. Night blindness: Usually not inherited. It is most commonly caused by a deficiency of vitamin A, which is needed to make rhodopsin, the pigment in the rod cells of the retina. It is an acquired, nutritional condition.
• E. Sickle cell anaemia: Inherited. It is caused by a mutated haemoglobin gene (HbS), which is passed on by parents who carry the gene.

Answer: The condition that is not inherited is night blindness, which is option D.

Exam tip: Remember that genetic conditions are the ones with a gene pattern: albinism (autosomal recessive), colour blindness and haemophilia (sex-linked), and sickle cell (haemoglobin gene). Conditions linked to a vitamin deficiency, such as night blindness (vitamin A), rickets (vitamin D), and scurvy (vitamin C), are not inherited.