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Katherine Johnson’s mathematical calculations helped guide some of America’s most important early space missions while she confronted the racial and gender barriers faced by Black women in twentieth-century America.
MORE →Reflects the personal views, recollections, and perspective of the author, Mike Davis.
This is a personal recollection on the Move fire on May 13, 1985
 | This article may be too technical for most readers to understand. (May 2022) |
A polygene is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait, thus contributing to multiple-gene inheritance (polygenic inheritance, multigenic inheritance, quantitative inheritance[1]), a type of non-Mendelian inheritance, as opposed to single-gene inheritance, which is the core notion of Mendelian inheritance. The term "monozygous" is usually used to refer to a hypothetical gene as it is often difficult to distinguish 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.[2] In July 2016, scientists reported identifying a set of 355 genes from the last universal common ancestor (LUCA) of all organisms living on Earth.[3]
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.
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. Allelic substitutions contribute to the variance in a specified quantitative character. 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.[4]
In modern sense, the inheritance mode of polygenic patterns is called polygenic inheritance, whose main properties may be summarized as follows:
Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect.[9] Examples of human polygenic inheritance are height, skin color, eye color and weight. Polygenes exist in other organisms, as well. Drosophila, for instance, display polygeny with traits such as wing morphology,[10] bristle count[11] and many others.
The frequency of the phenotypes of these traits generally follows a normal continuous variation distribution pattern. This results from the many possible allelic combinations. When the values are plotted, a bell-shaped "normal" curve is obtained. The mode of the distribution represents the optimal, or fittest, phenotype. The more genes are involved, the smoother the estimated curve, which follows from the Central Limit Theorem. This implies that traits such as height that are both highly heritable and normally distributed are necessarily polygenic. In other words, the fact that human height follows a smooth bell curve implies that there can be no single gene (or even small cluster of genes) that control height under ordinary circumstances. However, in this model all genes must code for alleles with additive effects. 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.[12]
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.[13]
Another interest of statistical geneticists using QTL mapping is to determine the complexity of the genetic architecture underlying a phenotypic trait. 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. This can provide information on how the phenotype may be evolving.
Source: Wikipedia. Article content is retrieved live through the MediaWiki API.
A polygene is a member of a group of non-epistatic genes that interact additively to influence a phenotypic trait, thus contributing to multiple-gene inheritance (polygenic inheritance, multigenic inheritance, quantitative inheritance), a type of non-Mendelian inheritance, as opposed to single-gene inheritance, which is the core notion of Mendelian inheritance. The term "monozygous" is usually used to refer to a hypothetical gene as it is often difficult to distinguish 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.
Polygenesis can refer to: Polygenesis (linguistics), a theory of language origin Polygenism, an obsolete theory of human origin Gene duplication, a form of genetic disorder resulting in the overexpression of a particular gene Polygenetic landforms, landforms formed the accumulative action of various processes
A pathosystem is a subsystem of an ecosystem and is defined by the phenomenon of parasitism. A plant pathosystem is one in which the host species is a plant. The parasite is any species in which the individual spends a significant part of its lifespan inhabiting one host individual and obtaining nutrients from it. The parasite may thus be an insect, mite, nematode, parasitic Angiosperm, fungus, bacterium, mycoplasma, virus or viroid. Other consumers, however, such as mammalian and avian herbivores, which graze populations of plants, are normally considered to be outside the conceptual boundaries of the plant pathosystem. A host has the property of resistance to a parasite. And a parasite has the property of parasitic ability on a host. Parasitism is the interaction of these two properties. The main feature of the pathosystem concept is that it concerns parasitism, and it is not concerned with the study of either the host or parasite on its own. Another feature of the pathosystem concept is that the parasitism is studied in terms of populations, at the higher levels and in ecologic aspects of the system. The pathosystem concept is also multidisciplinary. It brings together various crop science disciplines such as entomology, nematology, plant pathology, and plant breeding. It also applies to wild populations and to agricultural, horticultural, and forest crops, and to tropical, subtropical, as well as both subsistence and commercial farming. In a wild plant pathosystem, both the host and the parasite populations exhibit genetic diversity and genetic flexibility. Conversely, in a crop pathosystem, the host population normally exhibits genetic uniformity and genetic inflexibility (i.e., clones, pure lines, hybrid varieties), and the parasite population assumes a comparable uniformity. This distinction means that a wild pathosystem can respond to selection pressures, but that a crop pathosystem does not. It also means that a system of locking (see below) can function in a wild plant pathosystem but not in a crop pathosystem. Pathosystem balance means that the parasite does not endanger the survival of the host; and that the resistance in the host does not endanger the survival of the parasite. This is self-evident from the evolutionary survival of wild plant pathosystems, as systems, during periods of geological time. The gene-for-gene relationship is an approximate botanical equivalent of antigens and antibodies in mammals. For each resistance gene in the host, there is a corresponding, or matching, gene in the parasite. When the genes of the parasite match those of the host, the resistance does not operate. There are two kinds of resistance to parasites in plants: Vertical resistance involves a gene-for-gene relationship. This kind of resistance is genetically controlled by single genes, although several such genes may be present in a single host or parasite individual. Vertical resistance is ephemeral resistance because it operates against some strains of the parasite but not others, depending on whether or not a match occurs. In agriculture, vertical resistance requires pedigree breeding and back-crossing. It has been the resistance of choice during the twentieth century. Horizontal resistance does not involve a gene-for-gene relationship. It is the resistance that invariably remains after vertical resistance has been matched. It is genetically controlled by polygenes and it is durable resistance as many ancient clones testify. Its use in agriculture requires population breeding and recurrent mass selection. Infection is the contact made by one parasite individual with one host individual for the purposes of parasitism. There are two kinds of infection: Allo-infection means that the parasite originates away from its host and has to travel to that host. The first infection of any individual host must be an allo-infection. Vertical resistance can control allo-infection only. It normally does this with a system of locking (see below) which reduces the proportion of allo-infections that are matching infections. Auto-infection means that the parasite originates on, or in, the host that it is infecting. Auto-infection and all the consequences of a matching allo-infection, can be controlled only by horizontal resistance. This is because the parasite individual reproduces asexually to produce a clone (or else reproduces sexually and quickly reaches homogeneity of matching individuals) and auto-infection is thus matching infection. An epidemic is the growth of a parasite population which is made at the expense of the host population. There are two kinds of epidemic: Continuous epidemics have no break in the parasitism; they have no gene-for-gene relationships; they involve evergreen trees, and some perennial herbs. Discontinuous epidemics have regular breaks in the parasitism, due to an absence of host tissue during an adverse season, such as a temperate winter or tropical dry season; they often have a gene-for-gene relationship against some of their parasites; they involve annual plants, some perennial herbs, and the leaves and fruits of deciduous trees and shrubs.
Major gene is a gene with pronounced phenotype expression, in contrast to a modifier gene. Major gene characterizes common expression of oligogenic series, i.e. a small number of genes that determine the same trait. Major genes control the discontinuous or qualitative characters in contrast of minor genes or polygenes with individually small effects. Major genes segregate and may be easily subject to mendelian analysis. The gene categorization into major and minor determinants is more or less arbitrary. Both of the two types are in all probability only end points in a more or less continuous series of gene action and gene interactions. The term major gene was introduced into the science of inheritance by Keneth Mather (1941).
Before the 1921 destruction of Tulsa’s Greenwood District, Black residents had created a remarkable center of business and community life. The district included stores, professional offices, entertainment venues and homes owned by Black citizens. Understanding Greenwood means learning what was built—not only what was burned.
MORE →Brown v. Board of Education in 1954.