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?

Verified step by step guidance

1. Understand the genetic basis of Xeroderma pigmentosum (XP): XP is an autosomal recessive condition caused by mutations in genes responsible for repairing UV-induced DNA damage.
2. Recognize that multiple genes are involved in the repair of UV-induced DNA damage. These genes encode proteins that function in nucleotide excision repair (NER), a pathway critical for correcting UV-induced DNA lesions.
3. Identify the genetic phenomenon illustrated by XP: Since mutations in any one of several genes can lead to the same condition (XP), this is an example of genetic heterogeneity. Genetic heterogeneity occurs when mutations in different genes produce the same phenotype.
4. Consider the implications of genetic heterogeneity: In XP, different patients may have mutations in different genes, but all exhibit the same clinical symptoms due to the shared disruption of the DNA repair pathway.
5. Conclude that understanding genetic heterogeneity is important for diagnosing and treating XP, as different mutations may require different therapeutic approaches or genetic counseling strategies.

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance is a pattern of genetic transmission where two copies of a mutated gene, one inherited 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 genes 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 an accumulation of mutations, resulting in skin lesions and increased cancer risk. Understanding these mechanisms is crucial for grasping how XP develops.

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.