Answer:
20%
Explanation:
If a DNA molecule is double-stranded, the guanine base of one strand pairs with cytosine of another strand. Therefore, a double-stranded DNA always has the same proportions of guanine and cytosine ratio. This holds true for adenine and thymine bases as well which also form a complementary base pair. It is also called Chargaff's rule. Therefore, if a double-stranded DNA has 20% guanine, then the same DNA sample would have 20% of the cytosine base.
