Locus (genetics)
From Wikipedia, the free encyclopedia
(1) Chromatid. One of the two identical parts of the chromosome after S phase.
(2) Centromere. The point where the two chromatids touch, and where the microtubules attach.
(3) Short arm
(4) Long arm.
In biology and evolutionary computation, a locus is a fixed position on a chromosome, such as the position of a gene. 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 at some locus are called homozygous, while those that have different alleles at a locus, heterozygous.
[edit] Nomenclature
The chromosomal locus of a gene might be written "6p21.3".
| Component | Explanation |
| 6 | The chromosome number. |
| p | The position is on the chromosome's short arm (p for petit in French); q indicates the long arm. |
| 21.3 | The numbers following the letter represent the position on the arm: band 21, sub-band 3. The bands are visible under a microscope when the chromosome is suitably stained. Each of the bands is numbered, beginning with 1 for the band nearest the centromere. Sub-bands and sub-sub-bands are visible at higher resolution. |
A range of locations is specified in a similar way. For example, the locus of gene OCA1 may be written "11q14-q21", meaning it is on the long arm of chromosome 11, somewhere in the range of 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] External links
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