Question

A segment of DNA contains 1200 nucleotides, of which 200 have adenine base. How many cytosine bases are present in this segment of DNA?

• A. 100
• B. 200
• C. 400
• D. 800

Answer 1

The correct option is C 400

• According to Chargaff's rule, the proportion of adenine is equal to thymine and the proportion of cytosine is equal to guanine because they are complementary bases.
• There are 200 adenine bases. The number of thymine bases will be equal to adenine which is 200 bases.
• The total number of bases is 1200. So, the remaining bases are 1200-(200+200)= 800.
• From the 800 bases, the number of cytosine and guanine will be the same, which is equal to 400 bases each.
  

Thus, the correct answer is option C.