Know Genetics Knowgenetics nucleotides adenine, cytosine, guanine, and thymine nucleotides http://knowgenetics.org/nucleotides-and-bases/ adenine, cytosine, guanine, and thymine four distinct, normal bases Nucleotides and Bases - Genetics Generation http://knowgenetics.org/nucleotides-and-bases/ adenine, cytosine, guanine, and thymine nucleotides