DNA Replication and Repair

A 28-year-old male with a family history of early-onset colorectal cancer and polyposis presents for genetic screening. Molecular analysis suggests a defect in mismatch repair (MMR) genes. Which investigation would be the most appropriate initial confirmatory test for Lynch Syndrome?

A 28-year-old man with Hodgkin lymphoma is started on ABVD chemotherapy. Bleomycin causes oxidative DNA strand breaks that accumulate faster than the replication machinery can repair them. The structure marked **D** in the diagram is responsible for sealing nicks between Okazaki fragments. Which of the following best explains why bleomycin toxicity overwhelms this repair mechanism and leads to cell death?

Which of the following is the most common site of spontaneous DNA mutation in humans?

Regarding DNA repair mechanisms in eukaryotes, all of the following statements are true EXCEPT:

A 28-year-old man from rural Maharashtra presents with a 6-month history of progressive skin photosensitivity, severe sunburn after minimal sun exposure, and multiple pigmented macules on sun-exposed areas. Ophthalmologic examination reveals early corneal opacification. Genetic testing confirms biallelic mutations in the XPA gene. What is the most appropriate immediate next step in management?