DNA molecules consist of chemically linked sequences of the bases adenine, quinine, cytosine, and thymine, denoted A, G, C, and T. A sequence of 3 bases is called a codon. A base may appear more than once in a codon.

The bases A and G are purines, while C and T are pyrimidines.
How many codons are there whose first base is a purine and the second and third bases are pyrimidines?

I know the answer is 8, but why is it 8? Why is it 2^3?

Question

DNA molecules consist of chemically linked sequences of the bases adenine, quinine, cytosine, and thymine, denoted A, G, C, and T. A sequence of 3 bases is called a codon. A base may appear more than once in a codon.

The bases A and G are purines, while C and T are pyrimidines. 
               How many codons are there whose first base is a purine and the second and third bases are pyrimidines? 


I know the answer is 8, but why is it 8? Why is it 2^3?

triciaal · Answer

you might get a better response if you post in Biology. if this is an application probability then|dw:1443893477530:dw|