Xeroderma pigmentosum (XP) is an autosomal recessive condition characterized by moderate to severe sensitivity to ultraviolet (UV) light. Patients develop multiple skin lesions on UV-exposed skin, and skin cancers often develop as a result. XP is caused by deficient repair of DNA damage from UV exposure. Many genes are known to be involved in repair of UV-induced DNA damage, and several of these genes are implicated in XP. What genetic phenomenon is illustrated by XP?

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance is a pattern of genetic transmission where two copies of a mutated gene, one from each parent, are necessary for an individual to express a trait or disorder. In the case of Xeroderma pigmentosum (XP), individuals must inherit two defective copies of the gene responsible for DNA repair to exhibit symptoms, highlighting the importance of both alleles in the manifestation of the condition.

DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that identify and correct damage to the DNA molecules that encode an organism's genome. In XP, the deficiency in these repair pathways, particularly those that fix UV-induced damage, leads to the accumulation of mutations, resulting in increased sensitivity to UV light and a higher risk of skin cancers.

Genetic Phenotype

A genetic phenotype refers to the observable physical or biochemical characteristics of an organism, determined by both genetic makeup and environmental influences. In XP, the phenotype is characterized by extreme sensitivity to UV light and the development of skin lesions and cancers, illustrating how specific genetic mutations can lead to distinct clinical manifestations.