Multiple Choice
Which aspect of DNA allows scientists to distinguish between individuals?
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7. DNA and Chromosome Structure
DNA Structure
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In an analysis of the nucleotide composition of DNA, which of the following statements is always true for double-stranded DNA?
A
The amount of adenine equals the amount of thymine.
B
The amount of guanine equals the amount of adenine.
C
The amount of adenine equals the amount of cytosine.
D
The amount of cytosine equals the amount of thymine.
Verified step by step guidance1
Recall Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) always equals the amount of thymine (T), and the amount of guanine (G) always equals the amount of cytosine (C).
Understand that this equality arises because adenine pairs specifically with thymine via two hydrogen bonds, and guanine pairs with cytosine via three hydrogen bonds, maintaining base pairing complementarity.
Recognize that the total amount of purines (adenine and guanine) equals the total amount of pyrimidines (thymine and cytosine), but individual amounts of adenine and guanine or cytosine and thymine are not necessarily equal.
Analyze each statement in the problem: check if it aligns with Chargaff's rules and base pairing principles.
Conclude that the only statement always true for double-stranded DNA is that the amount of adenine equals the amount of thymine.
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