DNA (Deoxyribonucleic acid) is the message of heredity for every organism. DNA is composed by twisting 2 chains of nucleotide, forming a double helix shape.
There are 4 types of nucleotide, including Adenine (A), Cytosine (C), Guanine (G) and Thymine (T). Among the 4 bases, A, T and C, G are in a complementary relationship, enabling them to form a chemical bonding and eventually interlocks to form the double helix shape.
Complementary relationship refers to the combination of nucleotides. (A) nucleotide must pair up with (T), while (C) must pair up with (G).

Basic Knowledge(2): DNA Replication
Biotechnology(1): DNA Extraction
Biotechnology(2): Gel Electrophoresis
Biotechnology (3): Polymerase Chain Reaction
Species Identification