Question

In DNA, thymine always pairs with ....................
(1) Adenine
(2) Cytosine
(3) Guanine
(4) Thymine

Answer 1

Adenine and Thymine are always paired and Guanine and Cytosine are always paired. So, "A" pairs with "T", and "C" pairs with "G." So the question asks why does A pair with T. This is due to the chemical structure of each base. Adenine and Thymine establish two hydrogen bonds between them.