Which of the following are the four primary bases found in DNA?

• A. Adenine, guanine, cytosine, and uracil
• B. Adenine, thymine, cytosine, and guanine
• C. Adenine, cytosine, thymine, and inosine
• D. Adenine, thymine, uracil, and cytosine

Answer: (B)

The four primary bases found in DNA are adenine, thymine, cytosine, and guanine. These bases pair specifically—adenine pairs with thymine, and cytosine pairs with guanine—forming the rungs of the DNA double helix.

This pairing is essential for the replication of DNA and the proper encoding of genetic information, as each base can only bond with its complementary pair, ensuring that the genetic code is accurately transmitted during cell division.

In contrast, uracil is not found in DNA; it replaces thymine in RNA. Additionally, inosine is not one of the primary bases in either DNA or RNA but is instead a derivative that can play roles in specific contexts, such as tRNA. Therefore, the correct identification of the bases that are exclusively found in DNA is crucial for understanding the structure and function of genetic material.