The information of a chromosome is contained in a DNA (deoxyribonucleic acid) molecule. This molecule is formed by two complementary polynucleotide chains having the three-dimensional structure of a double helix. On cell division, the double helix is opened and each of the parent strands progressively transforms into a complete DNA double helix daughter molecule. The two DNA daughter molecules are identical replicas of the parent molecule. Genes are segments of DNA. Therefore, on cell division, replication of the genes parallels the replication of the DNA molecule and hence of the chromosome.