<span>1.
double helix model was proposed after getting the clue from chargaff rule
purines = pyramidines
2.
A = T ( this means A pairs with T)
G = C (this means G pairs with C)
A DNA strand with the sequence A-T-T-G-C-T is T-A-A-C-G-A
3.
In all the species the nucleic acid is made of phosphate , sugar , nitrogenous base (A,T,C,G)
only the number purines and pyrimidines vary.</span>
