The black lines represent the bonds between the phosphate groups of the nucleotides. These form the individual strands of DNA. The black circles or dots represent the phosphate groups. The blue squares represent the deoxyribose sugar and the triangles represent the nitrogenous bases and are therefore of different colors, one for each nucleotide. In addition, since the nucleotides are joined in the following way, the two chains are not equal but complementary.
Adenine - Thymine
Cytosine - Guanine
