Albinism is an expression of trait controlled by

1. Analyze the question The question asks what controls the expression of albinism, which is a lack of melanin pigment in the skin, hair and eyes.

2. Explain the concept Albinism is an inherited condition. It is caused by a gene that fails to produce the enzyme (tyrosinase) needed to make melanin. The allele for albinism is recessive, so a person shows albinism only when they inherit two copies of it (genotype aa), one from each parent.

• AA is normal pigmentation.
• Aa is normal pigmentation, but the person is a carrier.
• aa is albino.

3. Step-by-step solution

• Option A, Chromosomes: genes are carried on chromosomes, but "chromosomes" is too general. It does not say how the trait is controlled or expressed.
• Option B, Recessive genes: this matches. The trait appears only in the homozygous recessive condition.
• Option C, Dominant genes: this is wrong. If albinism were dominant, one albino parent would pass it on to most children. In reality, two normal-looking carrier parents (Aa × Aa) can have an albino child, with a 25% chance each time.
• Option D, Mutation: the allele originally arose through mutation, but the expression of the trait in a family is controlled by inheritance of the recessive gene.

4. Answer The correct option is B. Recessive genes.

5. Exam tip When you see "albinism", think "aa = albino". Other recessive traits that often appear in JAMB are sickle cell anaemia (SS is the sickle cell disease genotype) and haemophilia (X-linked recessive). If a question asks about a trait skipping generations, it is usually recessive.