What is the primary defect observed in xeroderma pigmentosum?

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Inherited in an autosomal dominant patternDeficiency in repairing DNA damage caused by ultraviolet lightUneven buildup of melanin within the basal cell layerThickening of the epithelium accompanied by elongated rete ridges

Explanation

Xeroderma pigmentosum is marked by a failure to correct DNA damage induced by ultraviolet radiation, leading to increased sensitivity to sunlight. It is not inherited in an autosomal dominant manner, nor is it primarily characterized by abnormal melanin distribution or epithelial thickening.