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Principles of Biology
Published in Arthur T. Johnson, Biology for Engineers, 2019
Mendelian experimental results were extremely simple, much simpler than many other real results. Although there are cases where traits are determined by two independent alleles, one dominant and one recessive, and Mendel happened to have observed these in his experiments, all is not that easy. There are cases of multiple alleles (human blood types are an example). There are cases of incomplete dominance and codominance when intermediate levels of biochemicals are either not sufficient to produce the full effect or when intermediate levels can produce the full effect. There is pleiotropy, where one gene can affect an organism in many ways, and there is epistasis, where one gene is affected by the presence of other genes. Antagonistic pleiotropy is the term applied to a gene that has a strong positive, normally reproductive, effect on the young, but an adverse impact on the old individual. Some organismal traits are determined by multiple genes, a condition known as polygenic inheritance. And, finally, there is genetic linking between genes located on the same chromosome. It is possible that the effect of a gene can depend upon which parent contributed the gene. Thus, the Mendelian model is one of the simplest of possible genetic models, but it is the place to start (Weiss, 2017).
Glossary of scientific and technical terms in bioengineering and biological engineering
Published in Megh R. Goyal, Scientific and Technical Terms in Bioengineering and Biological Engineering, 2018
Polygene is one of a number of genes, each of small effect, which together act to determine the phenotype of a quantitative trait. The result is continuous variation in the trait and a seemingly non-Mendelian mode of inheritance.
Posthumanism: Creation of ‘New Men’ Through Technological Innovation
Published in The New Bioethics, 2021
Two important difficulties in correlating genes with traits are: (i) the association of more than one gene with a particular trait, and (ii) the association of a gene with more than one trait. The polygenicity of most human traits is only one of the problems encountered when considering their modification by the manipulation of genes. Multiple gene inheritance refers to a group of genes that interact collectively to influence a phenotypic trait. These genes are referred to as a quantitative trait locus because the traits they affect correspond to quantitative characters whose phenotypes vary continuously and not in discretely identifiable types. An important property of these genes is that their individual effects are usually relatively small and interchangeable such that identical phenotypes may be displayed by a great variety of genotypes. In addition, the phenotypic expression of polygenic characters can be considerably modified by environmental influences.
Transhumanist Genetic Enhancement: Creation of a ‘New Man’ Through Technological Innovation
Published in The New Bioethics, 2021
Polygenes are non-epistatic genes that interact additively to influence a phenotypic trait. Polygenic inheritance occurs when one characteristic is controlled by two or more genes. Often, as discussed above, the genes are many in number but small in their individual effects (Glazier et al.2002). Many allelic combinations are possible, and as a result the frequency of these phenotypic traits follows a pattern of a normal continuous distribution; height, weight and skin colour are examples of multiple gene inheritance. The phenotypic expression of polygenic characters can undergo considerable modification by environmental influences; thus, a person may have a genetic tendency to be underweight or obese, but his or her actual weight will depend on diet and exercise, and these factors often play a greater role than genes. The enormous complexity of polygenic traits does not allow to predict that polygene studies will ever map all the quantitative trait loci present in the human genome; nonetheless, the development of new analytical and statistical tools and continued progress in obtaining more complete descriptions of the architecture of these loci, indicate that a complete mapping cannot be ruled out.
Prospects for limiting access to prenatal genetic information about Down syndrome in light of the expansion of prenatal genomics
Published in The New Bioethics, 2023
In 2012, the OBGYNs Howard Minkoff and Richard Berkowitz noted that because of advances in genetic technology over the previous decade, ‘3000 genetic tests were available’ in the prenatal period for ‘diagnosable entitles’ (Minkoff and Berkowitz 2014, p. 1336). Since then the advances have continued. Whole genome sequencing of the fetus now appears to be feasible (Kitzman et al.2012, Lau et al.2014) which means that, theoretically, prospective parents could have access to all of a fetus’s genetic information. Rapid prenatal exome sequencing is increasingly becoming available (NHS England 2021). Genome-wide association studies have given rise to techniques that allow for the calculation of the probability of phenotypes based on the contribution of many genetic variants across the genome – technologies of ‘polygenic risk scoring’ (Choi et al.2020). The comprehensiveness of genetic information, along with technologies that enable the seeming ability to interpret these results, mean that the genetic information available to prospective parents or their health care providers will not just be information about disease traits, but could include information about any biological characteristic for which there is a known genetic contribution. For example, in a review article about polygenic risk score analyses, the genetics researcher Shin Wan Choi and his colleagues discuss the heritability of ‘height’ as explained through polygenic analysis. In addition to being referred to as ‘Pandora’s box’, the sheer amount of prenatal genetic information that could be available in the near future has been referred to as ‘a flood’ of information (Minkoff and Berkowitz 2014, p. 1336) offering ‘too many choices’ to prospective parents (Menutti and Driscoll 2003), with the interpretation of this information described as ‘a maze’ (Minkoff and Berkowitz 2014, p. 1336).