Complementary

Complementary is a term related to genetics- whereby the DNA/RNA bases on opposite anti-parallel strands match up so that they are able to form a Hydrogen bond between them. For example, Adenine is complementary to either Thymine or Uracil so that when they are opposite each other on a strand they "complement" each other in structure and so can from 2 Hydrogen bonds between them. Similarly ,Cytosine and Guanine are complementary to each other in that they can form 3 Hydrogen bonds between them.