Genotype and Phenotype

9 Key excerpts on "Genotype and Phenotype"

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  Principles of Psychiatric Genetics

  • John I. Nurnberger, Jr, Wade Berrettini(Authors)
  • 2012(Publication Date)
  • Cambridge University Press

    (Publisher)

  Similarly, the same phenotype may have arisen from different genotypes. This important observation was contradictory to the genetic theory at that time, which endorsed the idea that there was a one-to-one correlation between genotype and its “consequential” phenotype. About the same time, Herman Nilsson-Ehle, a Swedish expert in plant breeding and genetics, provided evidence for genetic and nongenetic contributions to a continuous pheno- type on the basis of observations of seed colors in crosses of oats and wheat [1]. As we now know, a genotype is the composition of DNA sequences; in contrast, a phenotype represents observable charac- teristics of an organism, and is the joint product of both genotypic and environmental influences. In gen- etic diseases that are transmitted through the classic or Mendelian model, genotypes are usually indicative of phenotypes in terms of the presence or absence of the disease. However, this certain correlation between genotypes and phenotypes does not exist in complex genetic diseases. Recently, there has been a surge of interest in the use of endophenotypes in psychiatric research, although the concept was first introduced to the field of psychiatry by Gottesman and Shields more than three decades ago [2]. This has been driven by con- cerns about the limited success and relatively poor reproducibility of the current psychiatric genetic research approach, and the fact that current psychi- atric diagnostic systems, DSM or ICD, are primarily based on phenomenology and lacking of justification by etiology. Psychiatry’s classification systems describe heterogeneous disorders [3]. The brain is the most complex of all organs. It is subject to com- plex interactions not only among genes, proteins, cells, and circuits of cells, but also across individuals and their changing experiences [4]. As such, the phenotypic output from the brain, i.e. behavior, is not simply a sum of all its parts.

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  Psychology and Its Allied Disciplines

  Volume 3: Psychology and the Natural Sciences

  • M. H. Bornstein(Author)
  • 2013(Publication Date)
  • Psychology Press

    (Publisher)

  It is no doubt true that early hehaviorists were unduly enthusiastic about the learning processes they were discovering and neglected the subject of behavioral genetics. … In an important sense all behavior is inherited, since the organism that behaves is a product of natural selection. Operant conditioning is as much a part of the genetic endowment as digestion or gestation. The question is not whether the human species has a genetic endowment, but how it is to be analysed [pp. 43–44].

  I would add that the possibility of discovering the laws governing environmental effects on behavior depends on the assumption that genotypes place rather strict limits on phenolability. A degree of genetic determinism, at least at the species level, is essential for every psychological school from radical behaviorism to cognitive humanism. All must assume that the members of a species which interests them have some common characteristics. The real problems arise with respect to intraspecies differences in reaction to environmental stimuli. The extent and importance of genotype-environment interaction is perhaps the most central issue in the relations between psychology and genetics.

  GENOTYPE-ENVIRONMENT INTERACTION

  For the sake of clarity, I define genotype-environment interaction (GEI) in a statistical sense, the presence of nonadditive effects of a genetic and an environmental variable upon a phenotype. For the universal mutual involvement of genotype and environment in development, I use the word coaction . Interest in GEIs arises from the fact that they make it difficult to predict the effects of a treatment on a specific individual.

  GEIs: Animal Studies

  Henderson (1967) reported great genetic variability in the effects of mild (buzzer) or strong (shock) stress in an open field upon later emotionality in the same field. Control groups were unstressed but treated similarly otherwise. Observations were made on four inbred mouse strains and on their 12 reciprocal hybrids. Regarding the study as 16 separate experiments, identical except for the genotypes of the subjects, and using defecation as the index of emotionality, the following hypotheses were supported (N times): no effects of stress (6); emotion increases montonically with the amount of stress (2);controls less emotional than the two stressed groups which do not differ (3): strongly stressed animals are most emotional, mildly stressed are least, controls are intermediate (2); controls most emotional, buzzer group least, shocked intermediate (2); and, shocked most emotional, buzzer and controls the same (1). Critics might challenge the validity and generalizability of the emotionality test, but the important point is that any theory of the relation between prior stress and temperament could be supported by choosing the right subjects. What happens to general laws?

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  Social and Emotional Development in Infancy and Early Childhood

  • Janette B. Benson, Marshall M. Haith(Authors)
  • 2010(Publication Date)
  • Academic Press

    (Publisher)

  Nature of nurture – A term referring to gene–environment correlations, when genetic predispositions are associated with environmental factors. Phenotype – An observable trait or behavior. Pleitropy – When one gene influences more than one phenotype. Polymorphism – A common variation in the sequence of DNA among people. Proband – The primary or first person identified in a research study. Quantitative trait loci (QTL) – One gene, among many that influence a trait is normally distributed. Transcription – The process of making of an RNA copy of the DNA sequence from the chromosome, the first step in gene expression. Translation – The process by which RNA directs the production of amino acids and polypeptides, which ultimately form proteins. Introduction Historically, the field of psychology has generally dis-counted the importance of genetic factors. Early psycho-logical theories and research were heavily influenced by environmentalism, the notion that experience accounted for all traits. Gregor Mendel’s research on inherited pat-terns of traits in pea plants and Charles Darwin’s theories of the importance of evolutionary influences for the selec-tion of traits were, by and large, not incorporated into psychological research. Studies that explored genetic and environmental influences on humans were also disre-garded. Francis Galton was the first person to systemati-cally study the influence of genetic and environmental factors for a human behavior; he published a family study of genius (intelligence) in 1869. It was not until 251 the mid-1900s, however, that the field of psychology as a whole began to consider the importance of genetic factors. Based on a number of influential animal studies of learning and twin and adoption studies of behavior, the field of psychology gradually accepted that genetic factors were important for psychological traits.

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  Population Genetics and Microevolutionary Theory

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

    (Publisher)

  Part 2 Genotype and Phenotype 295 8 Basic Quantitative Genetic Definitions and Theory In Chapter 1, we introduced the three premises upon which population genetics is founded. In Chapters 2 through 7, we explored the roles of premise one, DNA replication, and premise two, DNA mutation and recombination, on the fate of genes through space and time. Many powerful evolutionary mechanisms were uncovered during this exploration of premises one and two, but our discussion of evolutionary mechanisms remains incomplete until we weave the third premise into this microevolutionary tapestry. The third premise is that the information encoded in DNA interacts with the environment to produce phenotypes (measurable traits of an individual). Premise one, DNA replicates, tells us that genes have an existence in time and space that transcends the individual. This transcendent behavior of genes does not imply that individuals are not important. The evolutionary fate of genes does depend on the individuals that carry the genes. DNA cannot replicate except through the vehicle of an individual living and interacting with its environment. Therefore, how an individual interacts with the environment plays a direct role in the ability of DNA to replicate. As pointed out in Chapter 1, the fact that DNA replication is sensitive to how an individual interacts with its environment is the basis of natural selection and adaptive evolution. Premise three says that you inherit a response to an environment, not traits per se. Thus, the envi- ronmental context in which individuals live and reproduce cannot be ignored if we want a full understanding of evolution. In this chapter and the following two, we will lay the foundation for understanding the relationship between Genotype and Phenotype, a relationship that is essential to understand before turning our attention to natural selection and adaptive evolution in the final chapters of this book.

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  Developmental Psychology

  • Amanda Ludlow, Roberto Gutierrez(Authors)
  • 2014(Publication Date)
  • Bloomsbury Academic

    (Publisher)

  Both the sperm and ova each contain only 23 chromosomes. This ensures that when the two cells meet, the resulting new organism has the correct 46 chromosomes. The genotype refers to all genes that are inherited whereas the pheno-type determines the actual expression of these genes. The phenotype includes both physical and non-physical traits including the height and colour eyes of a person but also the child’s temperament such as shy or anxious child. There are two factors that have been found to be impor-tant in determining how the genes are expressed: the interaction with other genes and also the influence of the environment on the genotype. Genes often consist of conflicting information and will work in addi-tive ways whilst others battle for dominance. When working in an additive manner, the difference between the genes is split such that a ‘tall’ gene and a ‘small’ gene will be averaged out. In other cases genes follow a dominant–recessive pattern. Eye colour is a good example of this dominant–recessive battle. If one parent hands down a dominant brown eye gene whilst another parent hands down the recessive blue eye gene, the dominant gene will win resulting in a child with brown eyes. However, the genetic blueprint can also be disrupted by environmental factors, starting when the child is in the uterus and continuing throughout life. Alcohol and drugs have frequently been shown to have an effect on a child’s development. For example, exposure to alcohol during pregnancy can cause birth defects including those found in foetal alcohol syndrome. Consistent features of foetal alcohol syndrome are permanent and diminished physical growth, abnormal position of and function of joints is common, whilst facial deformities – such as flat-tening of the cheekbones and short nose – may also be present.

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  Genetic Diversity and Human Behavior

  • J.N. Spuhler(Author)
  • 2017(Publication Date)
  • Routledge

    (Publisher)

  Psychological Research and Behavioral Phenotypes 1 Gerald E. Mcclearn

  THE RICH VARIETY of human behavior offers an essentially unlimited array of phenotypes for genetic investigation, and many diverse behavioral characters have already been investigated (see, for example, Fuller and Thompson, 1960). It is obvious, nevertheless, that only the most modest beginning has been made. There has recently been a striking increase in interest in behavioral genetics, and, in view of the accelerated research effort to be expected in the coming years, it appears appropriate to examine at this time some tactical and strategic considerations regarding the selection of phenotypes for future studies.

  It is true, of course, that in an interdisciplinary area, such as behavioral genetics, choice of phenotype is sometimes determined by overriding considerations of theoretical or practical interest, wherein any shortcomings of the trait in terms of convenience of analysis are cheerfully tolerated because of intrinsic value. These considerations will naturally take priority. On the other hand, a range of phenotypes may be available within the general area chosen for investigation, and among these there may be large differences in efficiency and appropriateness from the point of view of genetic analysis. It is for this situation that the following comments are offered.

  To begin, one might examine the more “successful” of the current phenotypes of human genetics to see if any general characteristic might be apparent. The first impression is that chance and serendipity play a large role in the discovery of phenotypes that are successful in the sense of opening new avenues of research or contributing fresh insights into the hereditary process. The discovery of PTC tasting, as is well known, was a fortuitous observation in a chemical laboratory (Fox, 1932). The description of phenylketonuria resulted from the recommendation of a mutual friend that the father of two defective children, who had described their unusual odor, consult Dr. Foiling, who was known to be interested in such things (Centerwall and Centerwall, 1963).

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  Human Development in the Twenty-First Century

  Visionary Ideas from Systems Scientists

  • Alan Fogel, Barbara J. King, Stuart G. Shanker(Authors)
  • 2007(Publication Date)
  • Cambridge University Press

    (Publisher)

  Assumptions of genetically determined ‘‘innate’’ or ‘‘hard-wired’’ behavior have gradually given way to the realization that genes cannot, in and of themselves, produce behavioral or psychological traits or characteristics. This more dynamic view of behavioral development, in which an individual’s interests and behavior are no longer seen to be independent of his or her activity, experience, or context, has not, however, been widely extended to other levels of development. While many scientists now appreciate that it is not accurate to speak about genes directly determining psychological characteristics like intelligence or personality, most continue to view the development of an individual’s physical traits 11 through the old lens of genetic determinism. Physical characteristics like hair color, eye color, height, or body type are examples of traits that continue to be attributed solely to genetic factors, thought to be directly caused by genes inherited from one’s parents. Thus, James’s blond hair, blue eyes, right-handedness, and tall stature are thought by many to be caused by the genes he inherited from his mother and father. This view of trait development is both simplistic and misleading, but continues to have a firm hold in the minds of many people. We now know that all traits, be they behavioral or physical, require the necessary contributions of both genetic and non-genetic factors. Developmental biologists have repeatedly demonstrated that the development of any trait or character is the consequence of a unique web of interactions among an individual’s genes, complex molecular interactions within and across cells, and the nature and sequence of the physical, biological, and social environments through which the indi- vidual passes during its development. These developmental dynamics must be included in any plausible account of how traits develop and change over the course of infancy, childhood, or adulthood.

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  An Introduction to Genetics for Language Scientists

  Current Concepts, Methods, and Findings

  • Dan Dediu(Author)
  • 2015(Publication Date)
  • Cambridge University Press

    (Publisher)

  2 Nature, nurture, and heritability In this chapter we approach, at a fairly abstract level, the fundamental questions concerning the relationships between the phenotype (the observable properties of individuals), the genotype and the environment. We discuss the paramount impor- tance of variation in studying these relationships and we define, estimate and discuss the meanings and misinterpretations of heritability. Far from being a simple concept, heritability will turn out to have some non-intuitive properties that make the interpretation of heritability estimates quite a tricky exercise. Likewise, we will discover that, in fact, all the related concepts and distinctions, such as innate and acquired, or nature and nurture, are fuzzy and far from their apparent clarity in every- day discourse. We will end with a very brief survey of heritability studies in speech and language. This chapter also introduces several fundamental concepts of statistics that are necessary for a proper understanding of many topics covered in this book. 2.1 Phenotype, genotype and environment It is unquestionable that both “nature” and “nurture” are required for the development of a linguistic human being. Lacking “nature” will limit lan- guage development no matter how much “nurture” there might be, as many a pet owner can easily confirm. This is seemingly supported by studies of chimps (such as Nim Chimpsky and Washoe) reared in conditions similar to those experienced by human babies and infants, but which nevertheless fail to go beyond a rather limited level of language usage. On the other hand, having “nature” but lacking “nurture” is equally devastating, as shown by the cases of children who, for various reasons, have not been exposed to language during the so-called critical period for language acquisition (a well- known case being Genie) and who fail to develop full-blown language despite considerable efforts. 7

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  The Cambridge Handbook of Personality Psychology

  • Philip J. Corr, Gerald Matthews(Authors)
  • 2020(Publication Date)
  • Cambridge University Press

    (Publisher)

  It is likely that genetic effects associated with these traits will be small and large sample sizes will therefore be required to detect any asso- ciation. By measuring specific traits, studies are able to harmonize phenotypes and pool analyses across cohorts. This will increase the power to detect genetic effects rele- vant to personality traits. With recent advances in both computing and availabil- ity of increasingly rich data sources, there has been a surge in the number of behavioral genetic studies investigating personality traits. Behavioral genetics has the potential to both quantify genetic influences on these traits, in add- ition to indirectly quantifying environmental influences (Munafò, 2009). Here we provide a synthesis of these behavioral genetic studies to date. We begin by reviewing current work investigating the heritability of personality traits. We also look at the results from genome-wide asso- ciation analyses of these traits to date and discuss the implications of these findings on the potential for applying Mendelian randomization to personality traits. ESTIMATING HERITABILITY In order to investigate the genetic contribution to a pheno- type, it is useful to first estimate its heritability (Box 1). Heritability is the proportion of variation in a phenotype which can be attributed to genetic differences; these esti- mates are specific to the particular context and the time- point at which they are estimated (Beam & Turkheimer, 2017; Davey Smith, 2011; Matthews & Turkheimer, 2017; Tropf et al., 2017). For example, if a trait has a heritability of 30%, then 30% of the variation in this trait is assumed to be due to genetic variation. However, although these estimates provide an idea of the size of the genetic com- ponent for a particular trait, they do not give us any infor- mation about which genes are likely to be responsible for it (Cesarini & Visscher, 2017).

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