what is polygenic disorder?
A hereditary issue that is brought about by the joined activity of more than one quality. Instances of polygenic conditions incorporate hypertension, heart disease, and diabetes. Since such scatters rely upon the concurrent nearness of a few qualities, they are not acquired as just as are single-quality sicknesses.
Polygenic diseases are caused by the joint contribution of a number of independently acting or interacting polymorphic genes; the individual contribution of each gene may be small or even unnoticeable.
- Single-gene disorders, where a mutation affects one gene. Sickle cell anemia is an example.
- Chromosomal disorders, where chromosomes (or parts of chromosomes) are missing or changed.
- Complex disorders, where there are mutations in two or more genes.
Genetic disorders may also be complex, multifactorial, or polygenic, meaning they are likely associated with the effects of multiple genes in combination with lifestyles and environmental factors. Multifactorial disorders include heart disease and diabetes.
Polygenic inheritance occurs when one character is controlled by two or more genes. Often the genes are large in quantity but small in effect. Examples of human polygenic inheritance are height, skin color, eye color, and weight.
A “polygene” or “multiple gene inheritance” is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait. The term monozygous is usually used to refer to a hypothetical gene as it is often difficult to characterize the effect of an individual gene from the effects of other genes and the environment on a particular phenotype. Advances in statistical methodology and high throughput sequencing are, however, allowing researchers to locate candidate genes for the trait. In the case that such a gene is identified, it is referred to as a quantitative trait locus (QTL). These genes are generally pleiotropic as well. The genes that contribute to type 2 diabetes are thought to be mostly polygenes. In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth.
Traits with polygenic determinism correspond to the classical quantitative characters, as opposed to the qualitative characters with monogenic or oligogenic determinism. In essence instead of two options, such as freckles or no freckles, there are many variations, like the color of skin, hair, or even eyes.
A polygenic locus is any individual locus that is included in the system of genes responsible for the genetic component of variation in a quantitative (polygenic) character. Allelic substitutions contribute to the variance in a specified quantitative character. A polygenic locus may be either a single or complex genetic locus in the conventional sense, i.e., either a single gene or closely linked block of functionally related genes.
In a modern sense, the inheritance mode of polygenic patterns is called polygenic inheritance, whose main properties may be summarized as follows:
- Most metric and meristic traits are controlled by a number of genetic loci.
- The main mode of nonallelic genes interaction in corresponding gene series is the addition of mainly small particular allele contributions.
- The effects of allelic substitution at each of the segregating genes are usually relatively small and interchangeable which results that identical phenotype may be displayed by a great variety of genotypes.
- The phenotypic expression of the polygenic characters is undergoing considerable modification by environmental influence.
- Polygenic characters show a continuous rather than discontinuous distribution.
- Balanced systems of polygenic inheritance in a population contain a great deal of potential genetic variability in the heterozygous condition and released by small increments through genetic recombination between linked polygenes.
Mapping polygenes
Example of a genome-wide scan for QTL of osteoporosis
Traditionally, mapping polygenes requires statistical tools available to help measure the effects of polygenes as well as narrow in on single genes. One of these tools is QTL-mapping. QTL-mapping utilizes a phenomenon known as linkage disequilibrium by comparing known marker genes with correlated phenotypes. Often, researchers will find a large region of DNA, called a locus, that accounts for a significant amount of the variation observed in the measured trait. This locus will usually contain a large number of genes that are responsible. A new form of QTL has been described as expression QTL (eQTL). eQTLs regulate the amount of expressed mRNA, which in turn regulates the amount of protein within the organism.
polygenic disorder (diabetes) are of many types
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