Familypedia
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[[Image:Chromarms.gif|thumb|Short and long arms]]
 
[[Image:Chromarms.gif|thumb|Short and long arms]]
[[Image:Chromosome.png|thumb|150px|Chromosome.<BR>(1) {{wp|Chromatid}}. One of the two identical parts of the chromosome after S phase.<BR>(2) {{wp|Centromere}}. The point where the two chromatids touch, and where the microtubules attach.<BR>(3) Short arm<BR>(4) Long arm.]]
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[[Image:Chromosome.png|thumb|150px|Chromosome.<BR>(1) [[Wikipedia:Chromatid|Chromatid]]. One of the two identical parts of the chromosome after S phase.<BR>(2) [[Wikipedia:Centromere|Centromere]]. The point where the two chromatids touch, and where the microtubules attach.<BR>(3) Short arm<BR>(4) Long arm.]]
 
[[Image:NF2.PNG|thumb|Example of bands]]
 
[[Image:NF2.PNG|thumb|Example of bands]]
In {{wp|biology}} and {{wp|evolutionary computation}}, a '''locus''' (plural '''loci''') is a fixed position on a {{wp|chromosome}}, such as the position of a {{wp|gene}} or a biomarker ({{wp|genetic marker}}). A variant of the DNA sequence at a given locus is called an {{wp|allele}}. The ordered list of loci known for a particular {{wp|genome}} is called a {{wp|genetic map}}. {{wp|Gene mapping}} is the process of determining the locus for a particular {{wp|biological trait}}.
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In [[Wikipedia:biology|biology]] and [[Wikipedia:evolutionary computation|evolutionary computation]], a '''locus''' (plural '''loci''') is a fixed position on a [[Wikipedia:chromosome|chromosome]], such as the position of a [[Wikipedia:gene|gene]] or a biomarker ([[genetic marker|genetic marker]]). A variant of the DNA sequence at a given locus is called an [[allele|allele]]. The ordered list of loci known for a particular [[Wikipedia:genome|genome]] is called a [[Wikipedia:genetic map|genetic map]]. [[Wikipedia:Gene mapping|Gene mapping]] is the process of determining the locus for a particular [[Wikipedia:biological trait|biological trait]].
   
{{wp|Diploid}} and {{wp|polyploid}} cells whose chromosomes have the same allele at some locus are called {{wp|homozygote|homozygous}}, while those that have different alleles at a locus, {{wp|heterozygote|heterozygous}}.
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[[Wikipedia:Diploid|Diploid]] and [[Wikipedia:polyploid|polyploid]] cells whose chromosomes have the same allele at some locus are called [[Wikipedia:homozygote|homozygous]], while those that have different alleles at a locus, [[Wikipedia:heterozygote|heterozygous]].
   
 
== Nomenclature ==
 
== Nomenclature ==
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| ''p'' || The position is on the chromosome's short arm (''p'' for ''petit'' in French); ''q'' indicates the long arm.
 
| ''p'' || The position is on the chromosome's short arm (''p'' for ''petit'' in French); ''q'' indicates the long arm.
 
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| ''21.3'' || The numbers following the letter represent the position on the arm: band 21, sub-band 3. The bands are visible under a {{wp|microscope}} when the chromosome is suitably stained. Each of the bands is numbered, beginning with 1 for the band nearest the {{wp|centromere}}. Sub-bands and sub-sub-bands are visible at higher resolution.
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| ''21.3'' || The numbers following the letter represent the position on the arm: band 21, sub-band 3. The bands are visible under a [[Wikipedia:microscope|microscope]] when the chromosome is suitably stained. Each of the bands is numbered, beginning with 1 for the band nearest the [[Wikipedia:centromere|centromere]]. Sub-bands and sub-sub-bands are visible at higher resolution.
 
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|}
 
 
A range of locations is specified in a similar way. For example, the locus of gene {{wp|OCA1}} may be written "11q1.4-q2.1", 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.
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A range of locations is specified in a similar way. For example, the locus of gene [[Wikipedia:OCA1|OCA1]] may be written "11q1.4-q2.1", 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 {{wp|telomere}} of the long arm of chromosome 2.
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The ends of a chromosome are labeled ''"ptel"'' and ''"qtel"'', and so ''"2qtel"'' refers to the [[Wikipedia:telomere|telomere]] of the long arm of chromosome 2.
   
 
== External links ==
 
== External links ==

Latest revision as of 08:57, 29 June 2009

Short and long arms

Chromosome.
(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.

Example of bands

In biology and evolutionary computation, a locus (plural loci) is a fixed position on a chromosome, such as the position of a gene or a biomarker (genetic marker). 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.

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 "11q1.4-q2.1", 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.

External links[]


This page uses content from the English language Wikipedia. The original content was at Locus (genetics). The list of authors can be seen in the page history. As with this Familypedia wiki, the content of Wikipedia is available under the Creative Commons License.