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In genetics, a locus (pl.: 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 ...
The role and degree of locus heterogeneity is an important consideration in understanding disease phenotypes and in the development of therapeutic treatment for these diseases. [1] The detection of causal genes for diseases impacted by locus heterogeneity is difficult with genetic analysis methods such as linkage analysis and genome sequencing. [9]
A quantitative trait locus (QTL) is a locus (section of DNA) that correlates with variation of a quantitative trait in the phenotype of a population of organisms. [1] QTLs are mapped by identifying which molecular markers (such as SNPs or AFLPs ) correlate with an observed trait.
Recessive genetic disorders include albinism, cystic fibrosis, galactosemia, phenylketonuria (PKU), and Tay–Sachs disease. Other disorders are also due to recessive alleles, but because the gene locus is located on the X chromosome, so that males have only one copy (that is, they are hemizygous ), they are more frequent in males than in females.
In order to qualify as a true gene, by this definition, one has to prove that the transcript has a biological function. [5] Early speculations on the size of a typical gene were based on high-resolution genetic mapping and on the size of proteins and RNA molecules. A length of 1500 base pairs seemed reasonable at the time (1965). [14]
Genetic heterogeneity occurs through the production of single or similar phenotypes through different genetic mechanisms. There are two types of genetic heterogeneity: allelic heterogeneity, which occurs when a similar phenotype is produced by different alleles within the same gene; and locus heterogeneity, which occurs when a similar phenotype is produced by mutations at different loci.
There are two distinctive mapping approaches used in the field of genome mapping: genetic maps (also known as linkage maps) [7] and physical maps. [3] While both maps are a collection of genetic markers and gene loci, [8] genetic maps' distances are based on the genetic linkage information, while physical maps use actual physical distances usually measured in number of base pairs.
An expression quantitative trait is an amount of an mRNA transcript or a protein.These are usually the product of a single gene with a specific chromosomal location. This distinguishes expression quantitative traits from most complex traits, which are not the product of the expression of a single gene.