Published by Australian Academy of Science
Glossary | The Human Genome Project – discovering the human blueprint

allele. Genes can exist in more than one form. Each different form of the same gene is called an allele. For example, in the case of seed shape, there is one allele that determines wrinkled seeds and another allele that determines round seeds.

base (in DNA). Any one of four nitrogenous (nitrogen-containing) bases (adenine, thymine, guanine and cytosine). The sequence of the bases in DNA determines the sequence of amino acids in all proteins found in living things.

base pairs. Two bases held together by weak chemical bonds. The double helix shape of DNA is dependent on its two strands being held together by the bonds between the base pairs. In DNA, the bases that pair are adenine with thymine and guanine with cytosine.

chromosome. A long DNA molecule that contains the genes of the organism. Chromosomes are visible in cells during cell division.

DNA (deoxyribonucleic acid). The nucleic acid forming the genetic material of all organisms with the exception of some viruses which have RNA. DNA is present in the nucleus and other organelles such as mitochondria and chloroplasts.

gene. The basic unit of inheritance. A gene is a segment of DNA that specifies the structure of a protein or an RNA molecule.

genetic diseases. Those diseases (malfunctions) that result from abnormalities in chromosomes or DNA, and are inherited.

genetic map (linkage map). A map showing the sequence of genes on chromosomes.

genome. The total genetic material of an individual or species.

linked. The association of traits that occurs when the genes coding for them are on the same chromosome.

locus (plural loci). The position on a chromosome of a gene or other chromosome marker.

map. A plan of the linear sequence of chromosomes.

mapping. Constructing a plan (or map) of the linear sequence of chromosomes.

physical map. A map showing the location of sites (loci) on a chromosome.