Short and long arms

Chromosome components:

(1) Chromatid
(2) Centromere
(3) Short (p) arm
(4) Long (q) arm

Example of bands

In the fields of genetics and evolutionary computation, a locus (plural loci) is the specific location of a gene or DNA sequence on a chromosome. A variant of the DNA sequence at a given locus is called an allele. The ordered list of loci known for a particular genome is called a genetic map. Gene mapping is the process of determining the locus for a particular biological trait.

Diploid and polyploid cells whose chromosomes have the same allele of a given gene at some locus are called homozygous with respect to that gene, while those that have different alleles of a given gene at a locus, heterozygous with respect to that gene.

[edit] Nomenclature

The chromosomal locus of a gene might be written "6p21.3".

A range of locations is specified in a similar way. For example, the locus of gene OCA1 may be written "11q1.4-q2.1", meaning it is on the long arm of chromosome 11, somewhere in the range from sub-band 4 of band 1, and sub-band 1 of band 2.

The ends of a chromosome are labeled "ptel" and "qtel", and so "2qtel" refers to the telomere of the long arm of chromosome 2.

[edit] See also

• Chromosomal translocation

[edit] External links

• Overview at ornl.gov

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