Phenotypic Expression

5 Key excerpts on "Phenotypic Expression"

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  eBook - ePub

  Progress and Challenges in Precision Medicine

  • Mukesh Verma, Debmalya Barh(Authors)
  • 2016(Publication Date)
  • Academic Press

    (Publisher)

  Phenotype is basically the characteristics or traits of an organism which can be observed or detected through some means, for example, organism’s appearance, physiological or biochemical responses, development and psychological behavior. These characteristics of organisms are primarily caused by the genotype that is the information encoded in the collection of genes. The term “phenotype” seems to be straightforward in its meaning but its concept is often complex. One can think that any trait dependent upon the genotype is a phenotype, for example, human blood groups represent different phenotypes that are the accurate representation of genotypes. However, in some cases the phenotypes are also being regulated by the environmental factors that range from the habitat of the organism to the other influencing molecules. These variations in phenotypes due to environmental factors are also known as “ecophenotypic variation.” In another version, the influences of all these including genotype, environment, and genotype–environment interactions have been implicated on phenotype. In human beings, cephalic or cranial index (ratio of the maximum width of the head multiplied by 100 divided by its maximum length) of children is observed to be related to the area where a child is born, irrespective of the child’s genotype or cultural heritage. Thus phenomenon like epigenetics (alterations in phenotypes from changes in chromosome without any change in genotype), dual inheritance (influence of genetic and cultural evolution), polyphenism (different phenotypes arise from same genotype), and maternal effect (influence of environment and genotype of mother) can produce the complexity in understanding the possible phenotypes of patients.

  In literature, the concept of “phenotype” is presented differently. At least five definitions of phenotype can be found in the literature (Mahner and Kary, 1997 ). This may be due to the fact that phenotypes can now be measured quantitatively; observations can be made on different biological levels such as at systems, tissues, cellular, and molecular levels and due to the availability of sophisticated evaluation procedures. This led to the change of concept in the medical field from “the observable traits of an organism” to the “deviations from normal physiology, morphology, or behavior.” This determines that phenotype detection in the medical context is by taking physical and psychological evaluation, diagnostic tests, imaging, etc., to make the diagnosis for a medical problem. The more comprehensive concept of a phenotype can now be presented as the collection of noticeable properties of an organism, representing its physiology, its morphology at different levels, including cellular, tissue, organ, and body levels, and its behavior, incorporating even features such as the gene transcription in response to the environmental factors (Nachtomy et al., 2007

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  Insect Phenotypic Plasticity

  Diversity of Responses

  • T N Ananthakrishnan, Douglas Whitman, T N Ananthakrishnan, Douglas Whitman, T N Ananthakrishnan(Authors)
  • 2005(Publication Date)
  • CRC Press

    (Publisher)

  Gene products create a cellular environment that can be influenced by external factors, including heat, light, nutrition, pH, toxins, pathogens, etc. In some cases, the environment can directly influence gene expression. But more often 2 Insect Phenotypic Plasticity externally induced changes in the internal environments of developing organisms alter their development, physiology, or behaviour, producing different phenotypes. Hence, the genotype does not give rise to the phenotype, but to a range of phenotypes. In other words, a phenotype is a biological system constructed by successive interactions of the individual genotype with the environment, in which development takes place. The norm of the reaction (Schlichting & Pigliucci, 1998) is the entire range, the whole repertoire of the variant pathways in development, that may occur in the carrier of a given genotype in all environments, favourable or unfavourable, natural or artificiar' (Dobzhansky, 1971). Thus, phenotypes are always the product of genes x the environment. Indeed, genes can never be separated from the environment, because even the chromosomes of an unfertilized egg reside in a cellular environment that was presumably influenced by the mother's physiological state, and continues to be influenced by prevailing environmental conditions. This leads to the realization that most traits or characteristics of organisms are plastic, i.e., they can be influenced by the environment. It also suggests that phenotypic plasticity functions in evolution, by initiating phenotypic variation, the raw product upon which natural selection acts. Natural selection selects among different phenotypes, not genes, and variation is an indispensable prerequisite of evolution. When the environment induces a novel phenotype, then natural selection can begin to act on that novelty. If that specific phenotype never occurs, then it cannot be selected for. Phenotypic plasticity then comes to assume an important place in evolution.

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  Ecology and Evolution of Dung Beetles

  • Leigh W. Simmons, T. James Ridsdill-Smith, Leigh W. Simmons, T. James Ridsdill-Smith(Authors)
  • 2011(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Chapter 6 Explaining Phenotypic Diversity: The Conditional Strategy and Threshold Trait Expression

  Joseph Tomkins1 and Wade Hazel2

  1 Centre for Evolutionary Biology, School of Animal Biology, University of Western Australia, Crawley, Western Australia

  2 Department of Biology, DePauw University, Greencastle, IN, USA

  6.1 Introduction

  Variation in Phenotypic Expression accounts for intraspecific diversity in an array of traits and behaviours across the animal kingdom, including caste, trophic, seasonal, dispersal and predator-induced polyphenisms, sex ratio investment (all reviewed in West-Eberhard, 2003; Roff, 1996), adaptations to sperm competition (Parker, 1990b) and the often spectacular alternative size-dependent reproductive phenotypes of males (Oliveira et al ., 2008). For nearly a century, the existence of such discrete phenotypic variation in natural populations has been of interest to ecological geneticists because it suggests a balance of selective forces at work (Sheppard, 1975). Specifically, it raises the intriguing question of why, over evolutionary time, one alternative phenotype does not drive the other extinct.

  Most of the classical ecological genetic studies of variation in nature – the coexistence of discrete differences in shell banding and colour in snails (Cain & Sheppard, 1954) and different mimetic forms characteristic of Batesian mimicry in butterflies (Clark & Sheppard, 1960) – have been aimed at understanding the kinds of selective forces that maintain discrete variation. Most of these studies concerned phenotypic differences that are due to the relatively straightforward expression of simple genetic differences.

  In the framework of evolutionary game theory, phenotypic differences that are linked to one or a few loci, and inherited in accordance with Mendelian ratios, have been termed alternative strategies (Gross, 1996; Maynard Smith, 1982). In such cases, negative frequency-dependent selection, where rare phenotypes have higher fitness than common ones, lies behind the maintenance of the phenotypic diversity seen within the population (Gross, 1996; Maynard Smith, 1982). For example, it has been shown recently that the survival of male colour morphs in wild populations of guppy (Poecilia reticulata ) is negatively frequency-dependent (Olendorf et al

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  Phenotypic Switching

  Implications in Biology and Medicine

  • Herbert Levine, Mohit Kumar Jolly, Prakash Kulkarni, Vidyanand Nanjundiah(Authors)
  • 2020(Publication Date)
  • Academic Press

    (Publisher)

  11 Phenotypic switching and its evolutionary consequences Dragan Stajic and Claudia Bank, Gulbenkian Science Institute, Oeiras, Portugal Abstract In this book chapter, we discuss the importance of phenotypic switching with respect to adaptation. Hereby, we focus on epigenetic mechanisms of phenotypic switching that are involved in gene expression regulation. We start by placing the discovery of phenotypic switching in the context of the history of evolutionary biology. We highlight how the controversy about whether phenotypic switching can contribute to adaptation arose. We then present a nonexhaustive list of examples of epigenetic phenotypic switching in nature. Finally, we discuss several evolutionary hypotheses about the role of phenotypic switching in adaptation to new and fluctuating environments, and give examples of how these hypotheses have been addressed experimentally. Keywords Phenotypic switching; evolution; adaptation; epigenetic inheritance; gene expression; mutation Biological systems are characterized by stunning diversity. This diversity is reflected in variation of observable characters (i.e., phenotypes) both between individuals within the same and between different species (Darwin, 1895). Studying how this variation among individuals in the same population is generated and maintained, and how it translates into the differences that we can observe within and between species is the essence of evolutionary biology. The main source of observable phenotypic diversity is genetic changes that are stably transmitted to subsequent generations (Fig. 11.1). Natural selection acts on these inherited phenotypes by preserving the beneficial and erasing the deleterious ones, causing a corresponding change in frequency of the underlying genetic determinants in the population. However, phenotypes can also be determined and maintained by molecular mechanisms that are independent from the underlying functional DNA sequence

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  Population Genetics and Microevolutionary Theory

  • Alan R. Templeton(Author)
  • 2021(Publication Date)
  • Wiley-Blackwell

    (Publisher)

  Although we frequently use such expressions as a “dominant allele” or “recessive allele,” such expressions are merely a linguistic short hand for describing the genotype–phenotype relationship in a particular environmental context. Dominance, recessiveness, etc. are NOT intrinsic properties of an allele. Context is always important when dealing with the relationship between genotype and phenotype. Basic Quantitative Genetic Definitions and Theory 301 Nature Versus Nurture? Does nature (the genotype) or nurture (the environment) play the dominant role in shaping an individual’s phenotype? From premise three, we can see that this is a false issue. Phenotypes emerge from the interaction of genotype and environment. It is this interaction that is the true cau- sation of an individual’s phenotype, and it is meaningless to try to separate genotype and environ- ment as distinct causes for the individual’s phenotype. However, in population genetics, we are often concerned with a population of individuals with much phenotypic variability. Accordingly, in much of population genetics, our concern centers on causes of phenotypic variation among indi- viduals within the deme rather than the causation of any single individual’s phenotype. Causes of phenotypic variation in a population are quite distinct from causes of individual phenotypes, and the nature/nurture issue is limited only to causes of variation. We will illustrate these statements by considering yet another “simple” Mendelian genetic disease: phenylketonuria or PKU. The enzyme phenylalanine hydroxylase catalyzes the amino acid phenylalanine to tyrosine and is coded for by an autosomal locus in humans. Several loss-of-function mutations have occurred at this locus (Scriver and Waters 1999; Scriver 2007), and homozygosity for loss of func- tion alleles is associated with the clinical syndrome known as phenylketonuria or PKU.

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