Key Terms for Cell Division

A length of DNA that codes for the production of a particular polypeptide or protein.

The name given to the full set of genes in a cell. The human genome consists of about 30 000 genes.

Diploid cells contain two versions of every gene.

Haploid cells contain one version of every gene.

A long single molecule of DNA, organised around proteins called histones. The largest human chromosomes contain about 4000 genes. Chromosomes exist in cells all the time but they can be seen only during cell division, when they condense and separate.

Chromosomes exist in pairs - humans have 23 pairs. Homologous chromosomes have the same genes at the same positions, but not necessarily the same versions of each gene.

During cell division, the DNA of a cell is replicated (copied). When the chromosomes condense, they therefore appear as double structures: each unseparated chromosome within such a pair is called a chromatid.

When two chromatids are genetically identical (as in mitosis), they are called sister chromatids.

A bivalent is a pair of homologous chromosomes that line up together, as they do during meiosis.

The position of a gene on a chromosome.

The process in which a molecule of mRNA is assembled on an active gene; mRNA thus becomes a mobile copy of the gene.

The process of converting the code of th mRNA into a protein. This is achieved by protein synthesis: amino acids are joined in a particular order to make a protein such as an enzyme.