Final answer:
According to Chargaff's rules, if Adenine makes up 22% of a DNA sample, then Cytosine will also make up 22% of the sample, because Adenine pairs with Thymine and Cytosine pairs with Guanine (A=T and C=G).
Step-by-step explanation:
If a DNA sample shows that Adenine is 22%, according to Chargaff's rules, the percentage of Cytosine present will also be 22% because Adenine pairs with Thymine and Cytosine pairs with Guanine. Since DNA is a double helix, the amount of Adenine is always equal to Thymine (A=T) and the amount of Cytosine is always equal to Guanine (C=G). Therefore, if Adenine is 22%, Thymine is also 22%. That leaves 56% of the DNA bases to be divided equally between Guanine and Cytosine, giving us 28% for each. However, since we know Adenine and Thymine are each 22%, this means Guanine and Cytosine are each 28%.
However, the question specifically asks for the percentage of Cytosine. This means we'll only focus on the Cytosine-Guanine pairing, and as mentioned before, Cytosine will be 22% if Adenine is 22%.