Birgid Schlindwein's

Hypermedia Glossary Of Genetic Terms

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Homology Similarities in DNA or protein sequences between individuals of the same species or among different species. These two types of homology are called paralogy and orthology.

See also the figure at NCBI.

Related Terms:
Similarity 1. In comparison of nucleic acid sequences, the extent to which two nucleic acid sequences have identical bases at equivalent positions, usually expressed as a percentage.
2. In comparison of protein sequences, the extent to which the amino acid sequences of two proteins have identical or functionally similar amino acids at equivalent positions, usually expressed as a percentage. See also identity.

Source: Mouse Genome Informatics Glossary

DNA sequence The relative order of base pairs, whether in a fragment of DNA, a gene, a chromosome, or an entire genome. See base sequence.
Protein A large molecule composed of one or more chains of amino acids in a specific order; the order is determined by the base sequence of nucleotides in the gene coding for the protein. Proteins are required for the structure, function, and regulation of the bodys cells, tissues, and organs, and each protein has unique functions. Examples are hormones, enzymes, and antibodies.
Species A group of organisms belong to the same biological species, if they are capable of interbreeding to produce fertile offspring. However the biological test of a species is not always available, and so there is also a morphological species concept based on anatomical similarities.
Orthology Describes the evolutionary origin of a locus. Loci in two species are said to be orthologous when they have arisen from the same locus of their common ancestor.
For example, gene A in species 1 and 2 are orthologous. In contrast, gene B1, which has arisen by gene duplication in species 2, is paralogous to gene B in species 1.

See also the figure at NCBI.

Paralogy Describes the evolutionary origin of a locus. A locus in two species is said to be paralogous when it has arisen by gene duplication in one species. Cf orthology.
For example, gene B1, which has arisen by gene duplication in species 2, is paralogous to gene B in species 1.

See also the figure at NCBI.

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Programming: Herbert Maier
Database: Birgid Schlindwein. Please contact me if you encounter any mistakes or if you are missing anything
© Dr. Birgid B. Schlindwein
last update of the database 10/01/2006