the DNA and is produced in a way analogous to DNA replication. The messenger that transmits the DNA's instructions to the protein production centre, the ribosome, is a molecule known as RNA. It is formed along partly "unzipped" sections of DNA and differs only subtly from it. The messenger RNA travels to the ribosome, where it links up with another form of RNA, transfer RNA, which bears amino acids. It is from these amino acids that the proteins are formed. The RNA molecules are merely code carriers and ensure that the amino acids link together in the correct sequence to form the protein type required. In this way DNA controls the workings of the whole cell and hence of the whole organism.
The DNA molecules in the cell nucleus are aggregated into structures called chromosomes, and specific groupings of nucleic-acid base sequences on the DNA give rise to specific traits in the organism. These groupings are called genes. Half the chromosomes in a creature's cells, and hence half its genes, come from its mother and half from its father. This is reflected in the alignment of the chromosomes during cell division. The chromosomes then are arranged in pairs, mother-donated ones aligned with identical father-donated ones so that comparable genes are side by side. Even though each gene in a pair contributes to the determination of a particular characteristic, one gene often masks the effect of another.