Multiple Choice
In the context of DNA, how many different sequences of eight bases can be formed using the four standard nucleotides (A, T, C, G)?
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1. Introduction to Genetics
Fundamentals of Genetics
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A DNA molecule contains 32% thymine. According to Chargaff's rules, what percentage of cytosine would be present in this DNA molecule?
A
32%
B
68%
C
36%
D
18%
Verified step by step guidance1
Recall Chargaff's rules, which state that in a double-stranded DNA molecule, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). This means $\%A = \%T$ and $\%G = \%C$.
Given that thymine (T) is 32%, use Chargaff's rule to determine that adenine (A) is also 32%, because $\%A = \%T = 32\%$.
Calculate the combined percentage of adenine and thymine: $\%A + \%T = 32\% + 32\% = 64\%$.
Since the total percentage of all four bases must add up to 100%, subtract the combined percentage of A and T from 100% to find the combined percentage of guanine and cytosine: $100\% - 64\% = 36\%$.
Finally, because guanine and cytosine are present in equal amounts, divide the combined percentage by 2 to find the percentage of cytosine: $\%C = \frac{36\%}{2}$.
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