In genetics, a locus (plural loci) is a specific, fixed position on a chromosome where a particular gene or genetic marker is located.[1] Each chromosome carries many genes, with each gene occupying a different position or locus; in humans, the total number of protein-coding genes in a complete haploid set of 23 chromosomes is estimated at 19,000–20,000.[2]
Genes may possess multiple variants known as alleles, and an allele may also be said to reside at a particular locus. Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus, while those that have different alleles at a given locus are called heterozygous.[3] The ordered list of loci known for a particular genome is called a gene map. Gene mapping is the process of determining the specific locus or loci responsible for producing a particular phenotype or biological trait. Association mapping, also known as "linkage disequilibrium mapping", is a method of mapping quantitative trait loci (QTLs) that takes advantage of historic linkage disequilibrium to link phenotypes (observable characteristics) to genotypes (the genetic constitution of organisms), uncovering genetic associations.
The shorter arm of a chromosome is termed the p arm or p-arm, while the longer arm is the q arm or q-arm. The chromosomal locus of a typical gene, for example, might be written 3p22.1, where:
22 = region 2, band 2 (read as "two, two", not "twenty-two")
1 = sub-band 1
Thus the entire locus of the example above would be read as "three P two two point one". The cytogenetic bands are areas of the chromosome either rich in actively-transcribed DNA (euchromatin) or packaged DNA (heterochromatin). They appear differently upon staining (for example, euchromatin appears white and heterochromatin appears black on Giemsa staining). They are counted from the centromere out toward the telomeres.
The position is on the chromosome's short arm (a common apocryphal explanation is that the p stands for petit in French); q indicates the long arm (chosen as next letter in alphabet after p; it is also said that q stands for queue, meaning "tail" in French[4]).
22.1
The numbers that follow the letter represent the position on the arm: region 2, band 2, sub-band 1. 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 loci 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 region 1 to sub-band 1 of region 2.
The ends of a chromosome are labeled "pter" and "qter", and so "2qter" refers to the terminus of the long arm of chromosome 2.
^Wood, E.J. (1995). "The encyclopedia of molecular biology". Biochemical Education. 23 (2): 1165. doi:10.1016/0307-4412(95)90659-2.
^Ezkurdia, Iakes; Juan, David; Rodriguez, Jose Manuel; Frankish, Adam; Diekhans, Mark; Harrow, Jennifer; Vazquez, Jesus; Valencia, Alfonso; Tress, Michael L. (2014-11-15). "Multiple evidence strands suggest that there may be as few as 19,000 human protein-coding genes". Human Molecular Genetics. 23 (22): 5866–5878. doi:10.1093/hmg/ddu309. ISSN 1460-2083. PMC4204768. PMID 24939910.
locus, genetics, genetics, locus, plural, loci, specific, fixed, position, chromosome, where, particular, gene, genetic, marker, located, each, chromosome, carries, many, genes, with, each, gene, occupying, different, position, locus, humans, total, number, pr. In genetics a locus plural loci is a specific fixed position on a chromosome where a particular gene or genetic marker is located 1 Each chromosome carries many genes with each gene occupying a different position or locus in humans the total number of protein coding genes in a complete haploid set of 23 chromosomes is estimated at 19 000 20 000 2 Parts of a typical chromosome 1 Chromatid 2 Centromere 3 Short p arm 4 Long q arm Genes may possess multiple variants known as alleles and an allele may also be said to reside at a particular locus Diploid and polyploid cells whose chromosomes have the same allele at a given locus are called homozygous with respect to that locus while those that have different alleles at a given locus are called heterozygous 3 The ordered list of loci known for a particular genome is called a gene map Gene mapping is the process of determining the specific locus or loci responsible for producing a particular phenotype or biological trait Association mapping also known as linkage disequilibrium mapping is a method of mapping quantitative trait loci QTLs that takes advantage of historic linkage disequilibrium to link phenotypes observable characteristics to genotypes the genetic constitution of organisms uncovering genetic associations Contents 1 Nomenclature 2 See also 3 References 4 External linksNomenclature Edit Cytogenetic banding nomenclature The shorter arm of a chromosome is termed the p arm or p arm while the longer arm is the q arm or q arm The chromosomal locus of a typical gene for example might be written 3p22 1 where 3 chromosome 3 p p arm 22 region 2 band 2 read as two two not twenty two 1 sub band 1Thus the entire locus of the example above would be read as three P two two point one The cytogenetic bands are areas of the chromosome either rich in actively transcribed DNA euchromatin or packaged DNA heterochromatin They appear differently upon staining for example euchromatin appears white and heterochromatin appears black on Giemsa staining They are counted from the centromere out toward the telomeres Example of cytogenetic bands Human karyotype with annotated bands and sub bands It shows 22 homologous autosomal chromosome pairs both the female XX and male XY versions of the two sex chromosomes as well as the mitochondrial genome at bottom left Further information Karyotype Component Explanation3 The chromosome numberp The position is on the chromosome s short arm a common apocryphal explanation is that the p stands for petit in French q indicates the long arm chosen as next letter in alphabet after p it is also said that q stands for queue meaning tail in French 4 22 1 The numbers that follow the letter represent the position on the arm region 2 band 2 sub band 1 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 loci 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 region 1 to sub band 1 of region 2 The ends of a chromosome are labeled pter and qter and so 2qter refers to the terminus of the long arm of chromosome 2 See also EditChromosomal translocation Cytogenetic notation Karyotype Null allele International System for Human Cytogenetic NomenclatureReferences Edit Wood E J 1995 The encyclopedia of molecular biology Biochemical Education 23 2 1165 doi 10 1016 0307 4412 95 90659 2 Ezkurdia Iakes Juan David Rodriguez Jose Manuel Frankish Adam Diekhans Mark Harrow Jennifer Vazquez Jesus Valencia Alfonso Tress Michael L 2014 11 15 Multiple evidence strands suggest that there may be as few as 19 000 human protein coding genes Human Molecular Genetics 23 22 5866 5878 doi 10 1093 hmg ddu309 ISSN 1460 2083 PMC 4204768 PMID 24939910 NCI Dictionary of Genetics National Cancer Institute Retrieved 13 December 2014 NCBI Genetics Review National Center for Biotechnology Information Retrieved 10 March 2021 Michael R Cummings 2011 Human Heredity Belmont California Brooks Cole External links Edit Wikimedia Commons has media related to Locus genetics Wikidata has the property cytogenetic location P4196 see uses Overview at ornl gov Chromosome Banding and Nomenclature from NCBI Retrieved from https en wikipedia org w index php title Locus genetics amp oldid 1125745769, wikipedia, wiki, book, books, library,
