Multiple Choice
Which of the following cell types has 23 unpaired chromosomes?
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3. Extensions to Mendelian Inheritance
Sex Chromosome
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If a male human analyzes his X chromosome and finds that it contains 30% thymine, what can he assume about the percentage of adenine on that X chromosome?
A
The percentage of adenine is 70%.
B
The percentage of adenine is also 30%.
C
The percentage of adenine is 15%.
D
The percentage of adenine is 20%.
Verified step by step guidance1
Recall Chargaff's rules, which state that in double-stranded DNA, the amount of adenine (A) equals thymine (T), and the amount of guanine (G) equals cytosine (C). This is because A pairs with T, and G pairs with C.
Understand that the problem involves analyzing the X chromosome DNA, which is double-stranded, so the base pairing rules apply.
Given that thymine (T) makes up 30% of the bases, use Chargaff's rule to conclude that adenine (A) must also make up 30% of the bases, since A pairs with T.
Recognize that the remaining 40% of the bases will be guanine (G) and cytosine (C) combined, but this is not directly relevant to finding the percentage of adenine.
Therefore, the percentage of adenine on the X chromosome is equal to the percentage of thymine, which is 30%.
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