(i) A DNA segment has a total of 1000 nucleotides, out of which 240 of them are adenine containing nucleotides. How many pyrimidine bases this DNA segment possesses?

(i) According to Chargaff s rule, ratio of purines to pyrimidines is equal, i.e. A + G = C + T

Since, the number of adenine (A) is equal to the number of thymine (T) and A = 240 (given)

Therefore, T = 240

Also, the number of guanine (G) is equal to cytosine ©. Thus, G + C = 1000 - (A + T)

G + C = 1000-480 = 520 Hence, G = 260, C = 260

The number of pyrimidine bases, i.e. C + T (2)

= 240 + 260 = 500