* Adenine (A) always pairs with Thymine (T)

* Guanine (G) always pairs with Cytosine (C)

This is due to the specific chemical structures of the bases and their ability to form hydrogen bonds.

* Adenine and thymine form two hydrogen bonds.

* Guanine and cytosine form three hydrogen bonds.

These specific pairings ensure that the two strands of DNA are complementary, meaning that they fit together perfectly. This is essential for DNA replication and transcription, where the DNA sequence is copied to create new DNA or RNA molecules, respectively.