Final answer:
All three conditions—breaking the DNA backbone, altering bases and base pairs, and incorporating incorrect bases during replication—contribute to increased cancer risk when DNA repair mechanisms fail. The correct answer is (D) I, II, and III.
Step-by-step explanation:
When DNA repair processes fail, increased risk of cancer can indeed follow. Each of the scenarios presented in the question—breaking the DNA backbone, altering bases and base pairs, and incorporating incorrect bases during replication—can lead to an increased risk of cancer.
Breaking the DNA backbone can result from ionizing radiation and can be severe because it can lead to large-scale chromosomal damage if not repaired correctly. Altering bases and base pairs can occur due to environmental factors like UV light or due to spontaneous mutations, potentially leading to changes in proteins that regulate cell growth. Lastly, incorporating the wrong bases during replication, despite the high fidelity of DNA polymerases, can introduce mutations which, if not corrected by proofreading or mismatch repair mechanisms, could result in oncogenic transformations.
Therefore, all three of the conditions listed can contribute to an increased risk of cancer when DNA repair is compromised. The correct answer to the question is (D) I, II, and III.