Final answer:
Erwin Chargaff discovered that DNA always had equal amounts of adenine (A) to thymine (T) and guanine (G) to cytosine (C), known as Chargaff's rules, which were pivotal in understanding DNA's structure and genetic function.
Step-by-step explanation:
The person who discovered that DNA always had equal amounts of the four bases was Erwin Chargaff, an Austrian biochemist. Chargaff's findings, known as Chargaff's rules, stated that the amount of adenine (A) is always equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C). This crucial piece of information supported the realization that DNA was the genetic material and played a significant role in the development of the double helix model by James Watson and Francis Crick.
Fascinatingly, Chargaff also found that while the concentrations of these nucleotide bases could vary from species to species, they did not vary within the same species or between individuals of the same species. This discovery was immensely useful for the understanding of DNA as a molecule responsible for genetic information.
Chargaff's findings were essential in guiding Watson and Crick to deduce the complementary base pairing mechanisms and the antiparallel nature of the two DNA strands in their double helix model. The consistency in base pairing across all species revealed the potential for DNA to carry complex genetic information, refuting the idea of DNA being a simplistic molecule.