Question

1. the double helix model of dna explained chargaffs rules because

a. adenine could hydrogen - bond with thymine and guanine could hydrogen - bond with cytosine to hold the helix together.
b. a helix repeats itself many times over, so the four bases in dna can repeat themselves many times.
c. adenine and thymine are found in one strand of the double helix and guanine and cytosine are found in the other strand.
d. adenine could change places with thymine while guanine could change places with

Explanation:

Chargaff's rules state that in DNA, the amount of adenine (A) equals thymine (T), and guanine (G) equals cytosine (C). The double helix model explains this because A forms hydrogen bonds only with T, and G forms hydrogen bonds only with C, ensuring their quantities are equal in the molecule. Option B is incorrect as repetition of the helix does not explain base pairing ratios. Option C is wrong because both strands contain all four bases, not separate pairs per strand. Option D is incomplete and incorrect, as bases do not swap places to maintain the rule.

Answer:

A. adenine could hydrogen-bond with thymine and guanine could hydrogen-bond with cytosine to hold the helix together.