Glossary

Electrophoresis
  A procedure which is used to separate molecules (DNA in the case of sequencing) according to their size. The separation takes place on a gel—which traps water in a polymer, and permits molecules to migrate in an electric field. Small molecules migrate faster than the large ones, which are slowed down. Molecules of DNA which differ in length by a single nucleotide can be separated on these gels.

Exon
  The majority of genes in plants and animals are fragmented. The biologically significant parts, the exons, are separated by intervening sequences without significance, the introns, which are eliminated in the messenger RNA. Finding the exon-intron boundaries is one of the major problems of annotation.

Gel
  See Electrophoresis.

Gene
  The functional unit of the genome. A gene corresponds to an instruction to be followed by the cell. The genome of a bacterium contains several thousand genes; that of plants or vertebrates (and therefore humans) consists of about 30 000 genes. Some genes code for RNA molecules with crucial functions in the cell, but the majority encode the sequences of proteins, which are synthesized via messenger RNA molecules (See RNA).

Genome
  The ensemble of the genetic information of an organism present in each of its cells. The material substance of genome consists of DNA (except in some viruses, which have RNA as their genetic material) in the form of long molecules called chromosomes.