If the base adenine constitutes 31% of an isolated DNA fragment, then write what…

If the base adenine constitutes 31% of an isolated DNA fragment, then write what will be the expected percentage of the base cytosine in it.
Explain how did you arrive at the answer given.

Ans.

To determine the expected percentage of the base cytosine in the isolated DNA fragment when adenine constitutes 31%, we can use Chargaff’s rules, which state that in double-stranded DNA, the amount of adenine (A) is equal to the amount of thymine (T), and the amount of guanine (G) is equal to the amount of cytosine (C).

Given that adenine constitutes 31% of the DNA fragment, we know that thymine also constitutes 31% (since they are complementary). Therefore, the total percentage of adenine and thymine together is 31% + 31% = 62%.

Since the total percentage of all bases in DNA is 100%, the remaining percentage after accounting for adenine and thymine is 100% – 62% = 38%.

According to Chargaff’s rules, the percentage of cytosine (C) is equal to the percentage of guanine (G). Therefore, the expected percentage of cytosine in the isolated DNA fragment is 38% / 2 = 19%.

So, the expected percentage of cytosine in the isolated DNA fragment is 19%.