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Gene Locus

DNA is the genetic code that establishes and codes for an organism's properties. This encompasses the organism's physiological, behavioural, and morphological characteristics. The distinct structures known as chromosomes are used for packaging and arranging DNA. A gene is a section of DNA that codes for a particular characteristic (although numerous genes may have an impact on a trait). On a chromosome, a gene has a defined location. The location of the gene on a certain chromosome is Locus(plural loci).

An exact, fixed location on a chromosome where a certain gene or genetic marker is found is known as a locus (plural loci) in genetics. The overall number of protein-coding genes in a full haploid set of 23 human chromosomes is believed to be 19,000-20,000. Each chromosome contains numerous genes, with each gene occupying a separate location or locus.

Gene Locus

Alleles are the different variations that genes might have. An allele is also said to dwell in a specific locus. Homozygous refers to a diploid or polyploid cell's chromosomes having the same allele at a specific location. In contrast, heterozygous refers to a cell's chromosomes having variable alleles at a particular locus. A gene map is an ordered list of the loci that are known for a certain genome. The process of finding the precise locus or loci responsible for a certain phenotypic or biological characteristic is known as gene mapping. In order to map quantitative trait loci (QTLs), a technique known as association mapping-also referred to as "linkage disequilibrium mapping"-uses historical linkage disequilibrium to connect phenotypes, or observable traits, to genotypes, or an organism's genetic makeup. This method identifies genetic associations.

Nomenclature of Gene Locus

Geneticists employ maps to pinpoint a specific gene's position on a chromosome. In one kind of map, the position of a gene is shown by its cytogenetic location. The cytogenetic location is determined based on a characteristic pattern of bands formed when chromosomes are dyed with certain reagents. The molecular location, an accurate description of a gene's location on a chromosome, is used in another kind of map. The molecular location is determined by the configuration of the DNA building units (nucleotides) that make up a chromosome.

Cytogenetic Location

The cytogenetic location of a gene is described by geneticists in a standardized manner. Most of the time, the location refers to a specific band's location on a stained chromosome:


If less information is available regarding the precise location, it may alternatively be expressed as a range of bands:


Gene Locus

The "address" of a gene on a chromosome is made up of a mixture of numbers and letters. There are numerous components to this address:

  • The chromosome containing the gene is represented by the first number or letter used to identify a gene's location. The autosomes, or chromosomes 1 through 22, are identified by their chromosomal number. The letters X or Y stand for the sex chromosomes.
  • The chromosome's arm- Based on the position of the centromere, which is a narrowing or constriction on each chromosome, each chromosome is split into two portions (arms). Conventionally, the shorter arm is known to be as p, and the longer arm as q. The second component of the gene's address is the chromosomal arm. For instance, Xp is the short arm of the X chromosome, while 5q is the long arm of chromosome 5.
  • Where the gene is located on the p or q arm- A gene's location may be identified based on a distinctive pattern of bright and dark bands that appears when the chromosome is dyed in a certain manner. Typically, a region and a band are represented by two numbers, occasionally with a decimal point and one or more additional digits (which indicate sub-bands within a bright or dark area). These digits are used to identify the position. With increasing distance from the centromere, the gene position number rises. For illustration, the long arm of chromosome 14's location 21 is designated as 14q21. The centromere is located closer to 14q21 than 14q22.
  • A gene's cytogenetic location is also sometimes denoted by the acronyms "cen" or "ter". The prefix "Cen" denotes how closely the gene is located to the centromere. For instance, the short arm of chromosome 16 close to the centromere is referred to as 16pcen. Terminus (abbreviated "Ter") denotes the gene near the p or q arm's end. For instance, the term "14qter" designates the extreme point of chromosome 14's long arm or its terminus. The CFTR gene is situated at 7q31.2 on the long arm of chromosome 7.

Molecular Location

The nucleotide order for each human chromosome was discovered by the Human Genome Project, an international scientific project that was finished in 2003. Because of sequencing information, researchers can now give many genes a more precise address than their cytogenetic location. The molecular address of a gene identifies the precise nucleotide position of that gene. It specifies the specific location of the gene on a chromosome and its size. Researchers can exactly determine how near or how distant a gene is from other genes on the same chromosome by understanding the molecular location.

Several research teams frequently give the molecular position of a gene slightly varied values. A gene's molecular address may differ slightly depending on the method used by researchers to analyse the human genome sequence.

Points to Ponder about Gene Loci

Gene Locus
  • Every chromosome comprises a lengthy DNA molecule with hundreds or thousands of distinct genes that code for various proteins.
  • A gene is a part of DNA that codes for a single polypeptide or protein.
  • The plural form of locus is loci, which refers to where a gene is located on a chromosome.
  • Scientists have been able to pinpoint the precise positions of the genes on various chromosomes using tests and genetic mapping procedures.
  • Each gene resides at a particular locus, ensuring that the gene responsible for a given trait is always located at the same location on a given chromosome.
  • Each gene might have two or more distinct versions known as alleles.
  • The nucleotide sequences of a gene's several alleles may change slightly, but they all reside at the same location (locus) on the chromosome.

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