Final answer:
Erwin Chargaff discovered that in DNA, adenine always pairs with thymine and cytosine with guanine, known as Chargaff's rules, which are crucial for DNA's structure and function.
Step-by-step explanation:
The question pertains to the discovery made by Austrian biochemist Erwin Chargaff, which states that in DNA, the amount of adenine (A) is always approximately equal to the amount of thymine (T), and the amount of cytosine (C) always matches that of guanine (G). This principle is known as Chargaff's rules. Adenine and thymine are complementary bases, just as cytosine and guanine are, and they pair together due to hydrogen bonding, forming the so-called steps of the DNA double helix.
Chargaff's findings were significant because they contributed to the understanding of DNA's double-helix structure, later modeled by James Watson and Francis Crick. Moreover, these pairings ensure the consistency of the DNA molecule's shape, which is crucial for the replication and function of DNA. The base pairings, A with T and G with C, are conserved across individuals of the same species, but the overall proportion of these base pairs can vary from one species to another, making it a tool for species identification.