Talk:Locus (genetics)

Language
Can anyone clarify the following paragraph please? I can't quite grasp what it is trying to say. (language difficulty?)

Each chromosome carries many genes; humans' estimated 'haploid' protein coding genes are 20,000-25,000, on the 23 different chromosomes. — Preceding unsigned comment added by 92.23.233.127 (talk) 04:06, 21 May 2014 (UTC)

So
So, what does p16INK4a (or even p16INK4a) mean? 82.18.21.208 10:10, 30 September 2006 (UTC)

What do you mean? That's not in the article. Maybe you should ask that question in the Reference Desk. Speaking of confusing stuff, what's with the fraction and symbols in the beginning? Is that part of the article? --JDitto 05:27, 27 November 2006 (UTC)
 * It looks like it was accidentally inserted during this edit. I have removed them. --Arcadian 05:35, 27 November 2006 (UTC)
 * Accidentally? Oh well. Thank you for your assistance. Have a nice day. --JDitto 05:43, 27 November 2006 (UTC)

In the last sentence of the first paragraph where it says that genome mapping is about saying what function is associated with a locus is reaching. Genome mapping is knowing what alleles are where. The purpose of these alleles is still largly unknown even as the Genome map is finished. So maybe it is true that, now, genome mapping wants to replace alleles with their biological function, but as the definition of mapping, this is reaching. Dave44000 21:47, 19 December 2006 (UTC)

Is 1 locus specific to a single gene?
I was wondering if someone could say whether there might be more than 1 gene at a locus. e.g. the locus used in the article, 6p21.3 I happen to know is CYP21 (21 hydroxylase), from the article I know that the locus is accurate to the sub-band, but how many genes are in a sub-band? Loci can be written to varying degrees of precision and I was thinking perhaps there should be something about precision in loci written from "chromosome 6" down to 6p21.3 and possibly beyond into sub-sub-bands. (I've never even seen seen "sub-sub-bands" before reading this article) --KX36 (talk) 14:00, 9 January 2008 (UTC)
 * I think you have a good question there. I would say that there can only be one gene in a locus since it is defined something like the specific position of a gene or other chromosomal marker. However, if you start talking about the number of genes in 6p21.3 there can most certainly be more than one (there is more than 50). I'm probably insulting somebody working with karyotypes here, but nowadays (post-human gene project) gene locations are mostly talked about in terms of bp-count from one gene. CYP21 (CYP21A2 - to be specific) would be said to be present at chr6:32114061-32117398. --LasseFolkersen (talk) 13:16, 18 March 2008 (UTC)
 * The article currently says a Loci can be made up of several genes, but every litterature I look it up in, says a single gene. So, should I correct that? --David Munch (talk) 11:22, 14 December 2008 (UTC)
 * There's such things as immunoglobulin lambda locus (IGL@) which has a number of genes. HGNC says IGL@ is at 22q11.2, but I've no idea whether it corresponds to a sub-band, a sub-sub-band or whatever. --ἀνυπόδητος (talk) 12:34, 28 January 2010 (UTC)

"ptel" or "pter"?
Hi! In the OMIM database and GenBank entries there are loci named "pter". Is this the same as "ptel"? I can't found a single entry named "ptel". Kind regards, —  Tirk·ﬂ  “…” 09:09, 2 September 2008 (UTC)
 * Wow - sure seems like an error to me, also, along with "qtel" rather than "qter". That error has been there for years....  Fixed.  ★NealMcB★ (talk) 00:38, 20 September 2011 (UTC)

nomenclature
So my question is, if the example 6p21.3 proveded in the article corresponds to chromosome 6, short arm, region 2, band 1, sub-band 3, then should that 6p21.3 be read as " six p two one point three" or as " six p twenty-one point three?" I came to this article to clarify that but the article doesn't specify.

So no one knows the answer to this question? — Preceding unsigned comment added by 162.82.215.201 (talk) 12:56, 21 March 2013 (UTC)


 * six p twenty-one point three--LasseFolkersen (talk) 07:00, 15 August 2013 (UTC)

Clarification required
I'm just starting to read up (on Wikipedia!) about genetics, so I really don't know much about the subject. Bearing that in mind could somebody expand/improve this sentence "A variant of the similar DNA sequence located at a given locus is called an allele". How dissimilar does similar have to be before it's considered an allele? Is it only an alelle if it's in a difference cell? Or only if it's on the second one of two "identical" chromosomes? Or either? The allele page suggests that the gene is called an allele regardless of whether it's different on two (diploid) chromosomes ... it's all very confusing to a beginner! I think it is the second or something you have just to keep looking that up on Google type in allele definition and I am wondering if prior to the world "genomicide" there have been more than 20,000 or above genes, have there once been perhaps 100,000 on them? So have we lost all our human developement heritage and are soon not only back to the emergence of Homo Sapiens genetically but to the misfit Pan separate species of the genus (that is the chimpanzee) and soon will develope correspondent incapacity or are intended to be "robotized"? ManyMore (talk) 14:46, 22 December 2015 (UTC)

Assessment comment
Substituted at 22:23, 29 April 2016 (UTC)

Ploidy and how it interacts with locus
I believe this page would be well suited to providing information on the relationship between ploidy and locus.

Confusion when reading the Wikipedia pages that concern genetics is caused by statements like, "If both alleles at a gene (or locus) on the homologous chromosomes are the same, they and the organism are homozygous with respect to that gene (or locus)." (wikipedia:Allele)

This example seems to refer to a gene as a single thing, with two locations, both called 'locus' in a manner that makes it also sound singular.

Is a gene in a diploid chromosome, a single logical entity located at two distinct locations on two separate 'arms'?

Is a locus a single name for a pair of locations on a diploid chromosome?

Clarifying this could then go on to clarify how a chromosome carries genetic information from both parents, even though each point in a sequence of DNA can only hold a single nucleobase which only holds a single bit of information, so it can't hold information from both parents. It seems to me that the genetics from one parent form one long and short arm set of a diploid chromosome, and the genetics from the other parent form the remaining long and short arm set. And that while these are sometimes referred to as chromosomes, and we have 46 of them, because they join in the middle, the pair are sometimes referred to as a single chromosome and we only have 23. Eltimbalino (talk) 13:46, 23 May 2017 (UTC)

@ sign
The article at sign says "In genetics, @ is the abbreviation for locus, as in IGL@ for immunoglobulin lambda locus." but there is nothing in this article to support that claim. Is it true? and if so, is there a citation for it? --John Maynard Friedman (talk) 00:05, 25 March 2021 (UTC)

Suggest to adopt, or allow for, more generic definition of "locus"
I suggest to allow for a more generic definition of "locus", i.e. 'a location on the genome where association with a trait or with multiple apparently unrelated traits is observed'. For instance in genome-wide association studies (GWASs), "loci" are usually/often defined based on linkage disequilibrium and/or physical distance between or among variants ("genetic markers" as per this lemma) (see, for an example, de Lange et al., Nature Genetics 2017:, Online Methods subsection "Locus definition"). (GWAS) loci are often denoted by the symbols of one or more genes, based on for instance the smallest physical distance to the lead variant or the highest likelihood (across different genes) that the gene of which the symbol is being used to denote the locus explains the observed association at the locus with the trait under consideration. An example of 'a' locus where multiple genes reside would be the "FADS" or "FADS1/2" locus, and for this reason I wouldn't agree with the current phrasing that "each gene occup[ies] a different position or locus". However, as there is no single, standardised definition of what denotes a "locus" in GWAS (as the example taken from de Lange et al., Nature Genetics 2017 above illustrates by its very existence, as it certainly wasn't the first GWAS publication to report on "loci"), although GWAS loci reported by different publications in scientific journals may be denoted by the same gene symbol, irrespective of any differences in used human reference genome builds, their actual physical location on the genome and for instance the identities (irrespective of any renaming of variants) and therefore positions of lead variants may differ across these publications. Therefore, in addition I'm not sure whether reference to a locus as "a specific, fixed position [on a chromosome]" is warranted. Lastly, the above also means that (at least in the GWAS context) the same 'locus' may associate with multiple seemingly unrelated traits, each of which may (at least in theory) have its own gene or genes that is/are deemed to be most likely to be causing the association observed at the 'locus', i.e. even if for instance the lead variant would be the same across the different GWAS analyses for the different seemingly unrelated traits (an example of this would be the "CPS1_ACADL" locus, which in that study associated with the serum levels of both an acylcarnitine and an amino acid). Statliner (talk) 15:45, 14 August 2021 (UTC)

who defined locus first?
I thought it was Morgan who first used the word locus to refer a position where a genetic trait reside, but I could not find any such description. Does any body knows who was the first? Sturtevant? Bellogalico (talk) 05:11, 19 May 2022 (UTC)