What is a gene?

Genes are small sections of DNA within the genome that code for proteins. They contain the instructions for our individual characteristics – like eye and hair colour. 

  • A gene is a small section of DNA that contains the instructions for a specific molecule, usually a protein.
  • The purpose of genes is to store information.
  • Each gene contains the information required to build specific proteins needed in an organism.
  • The human genome contains 20,687 protein-coding genes.
  • Genes come in different forms, called alleles.
  • In humans, alleles of particular genes come in pairs, one on each chromosome (we have 23 pairs of chromosomes). If the alleles of a particular gene are the same, the organism is described as homozygous for that gene. If they are different the organism is described as heterozygous for that gene.
  • An individual’s phenotype is determined by the combination of alleles they have.
  • For example, for a gene that determines eye colour there may be several different alleles. One allele may result in blue eyes, while another might result in brown eyes. The final colour of the individual’s eyes will depend on which alleles they have and how they interact.
  • The characteristic associated with a certain allele can sometimes be dominant or recessive.

This page was last updated on 2014-11-17