What genetic defects result in the disorder xeroderma pigmentosum (XP) in humans? How do these defects create the phenotypes associated with the disorder?

Key Concepts

DNA Repair Mechanisms

DNA repair mechanisms are cellular processes that correct damage to the DNA molecule. In xeroderma pigmentosum (XP), defects in nucleotide excision repair (NER) prevent the removal of UV-induced DNA lesions, leading to mutations. Understanding these mechanisms is crucial for grasping how XP results from an inability to repair DNA damage effectively.

Genetic Mutations

Genetic mutations are changes in the DNA sequence that can lead to altered protein function or expression. In XP, mutations in specific genes (such as XPA to XPG) disrupt the NER pathway, resulting in the accumulation of unrepaired DNA damage. This accumulation contributes to the phenotypes observed in XP, such as skin sensitivity and increased cancer risk.

Phenotypic Expression

Phenotypic expression refers to the observable traits or characteristics resulting from the interaction of an organism's genotype with its environment. In the case of XP, the genetic defects lead to a heightened sensitivity to UV light, resulting in skin lesions, pigmentation changes, and a predisposition to skin cancers. Understanding how these genetic defects manifest as specific phenotypes is essential for comprehending the disorder.