Polygene

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A polygene or multiple gene inheritance is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait. Polygene_sentence_0

The term "monozygous" is usually used to refer to a hypothetical gene as it is often difficult to characterise the effect of an individual gene from the effects of other genes and the environment on a particular phenotype. Polygene_sentence_1

Advances in statistical methodology and high throughput sequencing are, however, allowing researchers to locate candidate genes for the trait. Polygene_sentence_2

In the case that such a gene is identified, it is referred to as a quantitative trait locus (QTL). Polygene_sentence_3

These genes are generally pleiotropic as well. Polygene_sentence_4

The genes that contribute to type 2 diabetes are thought to be mostly polygenes. Polygene_sentence_5

In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth. Polygene_sentence_6

Traits with polygenic determinism correspond to the classical quantitative characters, as opposed to the qualitative characters with monogenic or oligogenic determinism. Polygene_sentence_7

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. Polygene_sentence_8

Overview Polygene_section_0

Polygenic locus is any individual locus which is included in the system of genes responsible for the genetic component of variation in a quantitative (polygenic) character. Polygene_sentence_9

Allelic substitutions contribute to the variance in a specified quantitative character. Polygene_sentence_10

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. Polygene_sentence_11

In modern sense, the inheritance mode of polygenic patterns is called polygenic inheritance, whose main properties may be summarized as follows: Polygene_sentence_12

Polygene_ordered_list_0

  1. Most metric and meristic traits are controlled by a number of genetic loci.Polygene_item_0_0
  2. Main mode of nonallelic genes interaction in corresponding gene series is addition of mainly small particular allele contributions.Polygene_item_0_1
  3. 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.Polygene_item_0_2
  4. The phenotypic expression of the polygenic characters is undergoing considerable modification by environmental influence.Polygene_item_0_3
  5. Polygenic characters show a continuous rather than discontinuous distribution.Polygene_item_0_4
  6. 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.Polygene_item_0_5

Inheritance Polygene_section_1

Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Polygene_sentence_13

Often the genes are large in quantity but small in effect. Polygene_sentence_14

Examples of human polygenic inheritance are height, skin color, eye color and weight. Polygene_sentence_15

Polygenes exist in other organisms, as well. Polygene_sentence_16

Drosophila, for instance, display polygeny with traits such as wing morphology, bristle count and many others. Polygene_sentence_17

Trait distribution Polygene_section_2

The frequency of the phenotypes of these traits generally follows a normal continuous variation distribution pattern. Polygene_sentence_18

This results from the many possible allelic combinations. Polygene_sentence_19

When the values are plotted, a bell-shaped curve is obtained. Polygene_sentence_20

The mode of the distribution represents the optimal, or fittest, phenotype. Polygene_sentence_21

The more genes are involved, the smoother the estimated curve. Polygene_sentence_22

However, in this model all genes must code for alleles with additive effects. Polygene_sentence_23

This assumption is often unrealistic as many genes display epistasis effects which can have unpredictable effects on the distribution of outcomes, especially when looking at the distribution on a fine scale. Polygene_sentence_24

Mapping polygenes Polygene_section_3

Traditionally, mapping polygenes requires statistical tools available to help measure the effects of polygenes as well as narrow in on single genes. Polygene_sentence_25

One of these tools is QTL-mapping. Polygene_sentence_26

QTL-mapping utilizes a phenomenon known as linkage disequilibrium by comparing known marker genes with correlated phenotypes. Polygene_sentence_27

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. Polygene_sentence_28

This locus will usually contain a large number of genes that are responsible. Polygene_sentence_29

A new form of QTL has been described as expression QTL (eQTL). Polygene_sentence_30

eQTLs regulate the amount of expressed mRNA, which in turn regulates the amount of protein within the organism. Polygene_sentence_31

Another interest of statistical geneticists using QTL mapping is to determine the complexity of the genetic architecture underlying a phenotypic trait. Polygene_sentence_32

For example, they may be interested in knowing whether a phenotype is shaped by many independent loci, or by a few loci, and do those loci interact. Polygene_sentence_33

This can provide information on how the phenotype may be evolving. Polygene_sentence_34


Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Polygene.