Albinism is an inherited condition in which the body makes little or no melanin, the pigment that colours skin, hair and the iris of the eye. People with albinism have very pale skin, white or very fair hair and pale eyes. They burn easily in sunlight, have a higher risk of skin cancer, and usually have poor eyesight because melanin is needed for normal eye development.The most common form is caused by a recessive allele of the gene coding for the enzyme tyrosinase. This enzyme catalyses an early step in converting the amino acid tyrosine into melanin. A mutation in the gene gives a non-functional enzyme, so melanin cannot be made.Albinism is autosomal recessive: the gene is on an autosome (not a sex chromosome), so males and females are affected equally, and only people with two recessive alleles are affected.• AA: normal pigmentation
• Aa: normal pigmentation, carrier
• aa: albinoOne functional allele makes enough tyrosinase, which is why the normal allele is dominant.Worked example: two carriers (Aa × Aa) have children. The offspring genotypes are 1 AA : 2 Aa : 1 aa, so each child has a ¼ chance of being albino and a ½ chance of being a carrier. In a pedigree, albinism typically skips generations and appears in children of two unaffected parents, the signature of a recessive allele.Albinism is found in many species, including mammals, birds and reptiles, where it follows the same pattern of inheritance.
• Aa: normal pigmentation, carrier
• aa: albinoOne functional allele makes enough tyrosinase, which is why the normal allele is dominant.Worked example: two carriers (Aa × Aa) have children. The offspring genotypes are 1 AA : 2 Aa : 1 aa, so each child has a ¼ chance of being albino and a ½ chance of being a carrier. In a pedigree, albinism typically skips generations and appears in children of two unaffected parents, the signature of a recessive allele.Albinism is found in many species, including mammals, birds and reptiles, where it follows the same pattern of inheritance.