AP BIOLOGY

Detailed explanation-1: -Further a 1:1 stoichiometric ratio of purine and pyrimidine bases (i.e., A+G=T+C ) should exist. This pattern is found in both strands of the DNA. They were discovered by Austrian-born chemist Erwin Chargaff, in the late 1940s.

Detailed explanation-2: -This sentence refers to the work of Erwin Chargaff, a biochemist at Columbia University. In the late 1940s, Chargaff analyzed the proportions of the four different types of base molecules in DNA, and found that DNA always contains equal amounts of guanine and cytosine, and equal amounts of adenine and thymine.

Detailed explanation-3: -Erwin Chargaff found that in DNA, the ratios of adenine (A) to thymine (T) and guanine (G) to cytosine (C) are equal. This parity is obvious in the final DNA structure.

Detailed explanation-4: -In tetranucleotide hypothesis, it stated that DNA was comprised of a number of repeats of guanine, adenine, cytosine, and thymine, and variations in the equimolar base ratios were due to experimental error.

Detailed explanation-5: -In 1949, Chargaff discovered that the proportions of bases in DNA depend on the species the DNA comes from. This was a major break from what scientists had believed until then.