DNA is the nearly universal genetic material. Experiments showing that DNA causes bacterial transformation and is the agent of virus production in phage-infected bacteria demonstrated this fact.
According to the Watson-Crick model, proposed in 1953 and confirmed in the succeeding decades, the DNA molecule is a double helix composed of two antiparallel strands of nucleotides; each nucleotide consists of one of four nitrogenous bases (A, T, G, or C), a deoxyribose sugar, and a phosphate. An A on one strand pairs with a T on the other, and a G pairs with a C.
DNA carries information in the sequence of its bases, which may follow one another in any order.
The DNA molecule reproduces by semiconservative replication. In this type of replication, the two DNA strands separate and the cellular machinery then synthesizes a complementary strand for each. By producing exact copies of the base sequence information in DNA, semiconservative replication allows life to reproduce itself.
Recombination arises from a highly accurate cellular mechanism that includes the base pairing of homologous strands of nonsister chromatids. Recombination generates new combinations of alleles.
