Locus ( genetics ) - wikipedia Locus ( genetics ) Chromosome components : ( 1 ) Chromatid ( 2 ) Centromere ( 3 ) Short ( p ) arm ( 4 ) Long ( q ) arm A locus ( plural loci ) in genetics is a fixed position on a chromosome, like the position of a gene or a marker ( genetic marker ). Each chromosome carries many genes ; human 's estimated ' haploid ' protein coding genes are 19,000 - 20,000, on the 23 different chromosomes. A variant of the similar DNA sequence located at a given locus is called an allele. The ordered list of loci known for a particular genome is called a gene 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 are called heterozygous with respect to that gene. Contents 1 Nomenclature 2 Centisome 3 See also 4 References 5 External links Nomenclature 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 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 1 Thus the entire locus of the example above would be read as `` three P two two point one. '' The cytogenetic bands count from the centromere out toward the telomeres. Component Explanation The chromosome number. p 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 ; alternatively it is sometimes said that q stands for queue meaning tail in French ). 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 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. Example of bands 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. Centisome A centisome ( not to be confused with a centrosome ) is defined as 1 % of a chromosome length. See also Chromosomal translocation Cytogenetic notation Karyotype Null allele International System for Human Cytogenetic Nomenclature References Jump up ^ Wood, E.J. ( 1995 ). `` The encyclopedia of molecular biology ''. Biochemical. Education. 23 ( 2 ) : 1165. doi : 10.1016 / 0307 - 4412 ( 95 ) 90659 - 2. Jump up ^ 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. Jump up ^ `` NCI Dictionary of Genetics ''. National Cancer Institute. Retrieved 13 December 2014. Jump up ^ Peter D. Karp ; Monica Riley ( 2009 - 01 - 11 ), Representations of Metabolic Knowledge ( PDF ) Michael, R. Cummings. ( 2011 ). Human Heredity. Belmont, California : Brooks / Cole External links Wikimedia Commons has media related to Locus ( genetics ). Wikidata has the property : cytogenetic location ( P4196 ) ( see talk ; uses ) Overview at ornl.gov Chromosome Banding and Nomenclature from NCBI. Retrieved from `` https://en.wikipedia.org/w/index.php?title=Locus_(genetics)&oldid=830036771 '' Categories : Chromosomes Talk Contents About Wikipedia Afrikaans Azərbaycanca Bân - lâm - gú Башҡортса Български Bosanski Català Čeština Dansk Deutsch Eesti Español Euskara فارسی Français Galego Hrvatski Bahasa Indonesia Italiano ქართული Қазақша Кыргызча Latviešu Magyar Македонски Nederlands 日本 語 Plattdüütsch Polski Português Română Русский Slovenčina Српски / srpski Srpskohrvatski / српскохрватски Suomi Svenska தமிழ் ไทย Türkçe Українська 中文 34 more Edit links This page was last edited on 12 March 2018, at 10 : 34. Text is available under the Creative Commons Attribution - ShareAlike License ; additional terms may apply. By using this site, you agree to the Terms of Use and Privacy Policy. Wikipedia ® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization. About Wikipedia

Question: where is the gene located in the chromosome
Answer: A locus