Introduction :
Chargaff Rule of base equivalence was established by Erwin Chargaff. It states that when DNA from any particular species is subjected to chemical hydrolysis in order to release its component purines and pyrimidines
(1) The total amount of adenine released is equal to the total amount of thymine and similarly, the total amount of cytosine is equal to the total amount of guanine.
i.e. A = T and
C = G
(2) It also states that in natural DNA the base ration A/T is closed to unity (=1) and C/G is also close to unity ( = 1)
i.e. (A/T) = (C/G) = 1
(3) A + G = T + C and
(4) A + C = G + T
Note : Ratio of [(A+T) / (C+G)] usually differs in Bacteriophage T2, it is 1.86 and Mycobacterium it is nearly 0.40