China
Africa
Explore chapters and articles related to this topic
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).
Evolutionary Computation
Published in Anand Nayyar, Dac-Nhuong Le, Nhu Gia Nguyen, Advances in Swarm Intelligence for Optimizing Problems in Computer Science, 2018
Anand Nayyar, Surbhi Garg, Deepak Gupta, Ashish Khanna
Molecular genetics provides a microscopic view of a natural evolution. It crosses the general visible phenotypic features, going deeper in the process. The key observation in genetics is the individual being a dual entity. The external feature is phenotypic properties, which are constructed at the level, i.e., internal construction. Genes here may be considered as the functional units of inheritance, encoding the phenotypic characters, i.e., the external factors visible, e.g., fur colour, trail length, etc. Genes may hold many properties from the possible alleles. An allele is one of the possible values a gene can have. Hence, an allele can be said to have a value that a variable can have mathematically. In a natural system, a single gene may affect many phenotypic traits, which is called pleiotropy. In turn, one phenotypic trait can be determined to be the result of a combination of many genes, termed ‘polygene.’ Hence, biologically the phenotypic variations are connected to the genotypic variations, which are actually an outcome of gene mutation, or the recombination of genes by sexual reproduction.
Ethical Considerations in Research with Genomic Data
Published in The New Bioethics, 2023
Rachel Horton, Anneke Lucassen
Genomic data are also used in research into common diseases. Sometimes, researchers take an approach similar to that used for rare disease, by analysing genomic data from families with very severe or early-onset forms of the disease with the aim of finding strong genetic risk factors that might represent therapeutic targets. However, often the intention is to identify a slew of genomic variations which each make a tiny contribution to an individual’s risk of developing a particular disease but in combination say something more significant about risk. These might then be candidates for inclusion in polygenic risk scores aiming to identify people at high or low risk for common diseases, though some challenge whether such scores will ever be sufficiently discriminatory to usefully augment existing successful screening programmes (Wald and Old 2019, Sud et al. 2021).
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.