DOCSLIB.ORG

A Joint History of the Nature of Genetic Variation and the Nature of Schizophrenia KS Kendler

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
A Joint History of the Nature of Genetic Variation and the Nature of Schizophrenia KS Kendler Molecular Psychiatry (2015) 20, 77–83 © 2015 Macmillan Publishers Limited All rights reserved 1359-4184/15 www.nature.com/mp EXPERT REVIEW A joint history of the nature of genetic variation and the nature of schizophrenia KS Kendler This essay traces the history of concepts of genetic variation and schizophrenia from Darwin and Mendel to the present. For Darwin, the important form of genetic variation for evolution is continuous in nature and small in effect. Biometricians led by Pearson agreed and developed statistical genetic approaches utilizing trait correlations in relatives. Mendel studied discontinuous traits and subsequent Mendelians, led by Bateson, assumed that important genetic variation was large in effect producing discontinuous phenotypes. Although biometricians studied ‘insanity’, schizophrenia genetics under Kraepelin and Rüdin utilized Mendelian approaches congruent with their anatomical-clinical disease model of dementia praecox. Fisher showed, assuming many genes of small effect, Mendelian and Biometrical models were consilient. Echoing prior conflicts, psychiatric genetics since then has utilized both biometrical models, largely in twins, and Mendelian models, based on advancing molecular techniques. In 1968, Gottesman proposed a polygenic model for schizophrenia based on a threshold version of Fisher’s theory. Since then, rigorous studies of the schizophrenia spectrum suggest that genetic risk for schizophrenia is more likely continuous than categorical. The last 5 years has seen increasingly convincing evidence from genome-wide association study (GWAS) and sequencing that genetic risk for schizophrenia is largely polygenic, and congruent with Fisher’s and Gottesman’s models. The gap between biometrical and molecular Mendelian models for schizophrenia has largely closed. The efforts to ground a categorical biomedical model of schizophrenia in Mendelian genetics have failed. The genetic risk for schizophrenia is widely distributed in human populations so that we all carry some degree of risk. Molecular Psychiatry (2015) 20, 77–83; doi:10.1038/mp.2014.94; published online 19 August 2014 …Variations, as Darwin and most breeders recognized, were of the faith that despite a current inability to discern pathological two types. There were sports, large discontinuous variations, lesions, the disorders were still fundamentally ‘organic’ and the relatively rare … [and] there were the less obvious but more ‘lesions’ might, in the meantime, be defined using physiological pervasive and plentiful minor variations which occurred in or psychological concepts (for example, ‘irritation’ or ‘negative 2 every character of the organism. (Provine,1 p. 5) symptoms’). This definition was based on a promissory note that individual psychotic disorders reflected distinct diseases which This essay sketches a joint history of the concepts of genetic would one day be traced to discrete pathological processes. variation and schizophrenia from the time of Darwin and Mendel This approach remained dominant in the 20th century as in the mid-19th century to the present. The nature of genetic illustrated by the following from the famous German psychiatrist, variation can be thought of both at the individual level (Are most Kurt Schneider: important differences in individuals the result of single genes of large effect or many genes of small effect?) and at the population We do not know the disease processes underlying cyclothymia level (Is the distribution of genetic liability normal or very bumpy [his term for manic-depressive illness] and schizophrenia. with a small proportion of individuals at high risk and the rest at However, diseases do underlie them. The frequent hereditary low risk?). nature, the fact that most of these disease run in families, the general physical changes often present … [and] above all … they destroy cohesion, interrupt the meaningful order, the THE PARADIGM OF PSYCHIATRIC ILLNESS continuity of meaning which characterizes normal develop- 5 The origin of our current anatomical-clinical concept of schizo- ment of life. (Moran and Smith, p. 377) phrenia arose in Europe in the late 19th century.2 Major influences included the discovery of microbial causes of disease and the One of Schneider’s prominent justifications for this biomedical associated move toward etiological models of illness,3 the rise of view of psychiatric illness is the hereditary/familial nature of the neuropathology and the ability to observe directly brain lesions, disorders. and the successful century long search for the cause of general paresis of the insane.4 Key features of this anatomo-clinical view of psychiatric illness included: (i) the rejection of unitary models THE BIOMETRICIANS of psychosis in favor of distinct diseases; (ii) an emphasis on Darwin’s theory of natural selection assumed widespread small symptom clusters, anatomical lesions and natural history; and (iii) trait variations in biological populations that impacted on fitness Departments of Psychiatry, and Human and Molecular Genetics, Virginia Institute of Psychiatric and Behavioral Genetics, Medical College of Virginia/Virginia Commonwealth University, Richmond, VA, USA. Correspondence: Dr KS Kendler, Psychiatry, Virginia Commonwealth University, VCU PO Box 980126, Richmond, 23298-0126 VA, USA. E-mail: [email protected] Received 18 March 2014; revised 30 April 2014; accepted 24 June 2014; published online 19 August 2014 History of nature of genetic variation and schizophrenia KS Kendler 78 and were transmitted across generations. A major debate In 1900, Mendel’s 1866 monograph was ‘rediscovered’ and his emerged in the late 19th century about whether this key assump- theory widely publicized, largely, because it fit well into the tion was correct.1 Did evolution act slowly on quantitative evolutionary framework of the re-discoverers. We will focus on variation or was it saltative, based on large changes (called one of them, Bateson, who became the ardent champion of ‘sports’)? Mendelism and saltative views of evolution in the Anglophonic Darwin’s cousin, Galton, had a complex role in this debate. He world.11,12 Evolution, he asserted, arose not from gradual small founded the field of human behavior genetics in his book shifts in quantitative characteristics but from large phenotypic ‘Hereditary Genius’ published 10 years after Darwin’s ‘Origin’.6 He changes in ‘one bound’. laid the groundwork for the ‘Biometrical approach’ to genetics by Given his viewpoints, it makes sense that Bateson greeted the collecting data in human relatives for a range of metrical traits and rediscovered Mendel with enthusiasm. Here was a biological basis encouraging similar work in other organisms. He prompted his for his saltative evolutionary view. The key concept of the younger and better mathematically trained associate, Pearson, to Mendelians, captured in their first ‘law’, was that the gene had a examine these data. From these efforts emerged our modern ‘unit character’ and was transmitted intact from generation to methods of regression and correlation. However, Galton disagreed generation. Furthermore, the effect of these unit characters with his more famous cousin about the nature of evolution, was large, producing distinct changes. At this early stage of favoring the theory of saltative evolution. Mendelism, the Mendelians assumed a one-to-one relationship Pearson, however, who emerged as the intellectual leader of between what we would now call ‘genotype’ and ‘phenotype’. the ‘Biometrical Geneticists’ in the last decade of the 19th century, Each gene affected one phenotype. Each phenotype was con- was a fervent Darwinian, convinced that continuous phenotypes trolled by one gene. were the material on which evolution worked, producing slow changes over long time intervals. The proper approach to genetics, he asserted, was to examine the association between THE START OF PSYCHIATRIC GENETICS continuous phenotypes in relatives—hence, the focus of the Modern psychiatric genetics began with the work of Ernst Rüdin Biometricians on their new ‘high-tech’ genetic tool: the correlation in the first decade of the 20th century. His daughter wrote: coefficient. This statistical technique assumed that the trait (and ‘Impressed by the recent rediscovery of the Mendelian laws, Rüdin implicitly the underlying genetic variation) was approximately hoped that by using the correct genetic methods, he would be normally distributed. able to uncover the proper Mendelian ratios for schizophrenia’. However, Pearson soon realized that this concept could be (Zebrin-Rudin and Kendler,13 p. 334) He began the first systematic applied to a dichotomous phenotype, assuming that it reflected family study of psychiatric illness in 1907 using admissions with a threshold imposed on an underlying normal distribution. definite schizophrenia to the Munich Psychiatric University He described this method in a 1901 essay ‘Mathematical Clinic.14 This study was undertaken in the same decade that the contributions to the theory of evolution VII, on the correlation very first of human medical traits including brachydactylism, of characters not quantitatively measurable’7 and called it a hemophilia, night-blindness and eye color were shown to have ‘tetrachoric correlation’. While it might seem common-sense to Mendelian segregation patterns.12 assume that discrete traits had to be due to discrete genes, nature Rüdin’s study utilized then ‘cutting edge’ methods of proband did not have to work that way. and age corrections, but included no control group.
Load more

Recommended publications
  • K-Model – an Evolutionary Algorithm with New Schema of Representation
    K-MODEL – AN EVOLUTIONARY ALGORITHM WITH NEW SCHEMA OF REPRESENTATION Halina Kwasnicka Department of Computer Science, Wroclaw University of Technology Wyspianskiego 27, 50-370 Wroclaw, Poland tel. (48 71) 3202397, fax: (48 71)211018, e-mail: [email protected], http://www.ci.pwr.wroc.pl/~kwasnick ABSTRACT The paper presents an evolutionary model with pleiotropy and polygene effects, named K-Model. Genes are integer numbers and the linear dependence between phenes and genes are assumed. The redundant genes, i.e., not active ones during some period of evolution, are also included. Such representation allows the evolutionary algorithm to escape from local optima (evolutionary traps) and evolve quicker especially for multi-modal and multi-variable fitness functions. INTRODUCTION From centuries people learn observing natural processes. Usually natural processes are perceived as very skilful, and researchers willingly imitate them to obtain effective techniques. Optimisation techniques called Genetic Algorithms (GAs), or more generally, Evolutionary Algorithms (EAs), base on biological evolution. They imitate the Darwinian paradigm survival the fittest, and use a vocabulary borrowed from genetics. GAs search large spaces efficiently without complete knowledge of an objective function. They require only a limited number of values of objective function to guide their search process. Operators analogical to genetic ones as crossover and mutation are used for achieving a new area in the search space (new solutions). GAs act on the set of coded potential solutions (called chromosomes or individuals) and use the strategy of natural selection to achieve their aims. Proposed by J. Holland genetic algorithms, which we call here as Classic Genetic Algorithm (CGA) uses a binary alphabet for defining chromosomes.
    [Show full text]
  • Karl Jaspers: the Icon of Modern Psychiatry
    Isr J Psychiatry - Vol. 54 - No 2 (2017) Karl Jaspers: The Icon of Modern Psychiatry Michael A. Schwartz, MD,1 Marcin Moskalewicz, PhD,2 and Osborne P. Wiggins, PhD3 1 Department of Psychiatry, Texas A&M Health Science Center College of Medicine, Round Rock, Texas, U.S.A. 2 Faculty of Philosophy, University of Oxford, and the Department of Social Sciences, Poznan University of Medical Sciences, Poznań, Poland 3 Department of Philosophy, University of Louisville, Louisville, Kentucky, U.S.A. modern scientific psychiatry. In their “Emil Kraepelin: ABSTRACT Icon and Reality” (1), the authors Eric J. Engstrom and Kenneth S. Kendler challenge the so-called neo-Kraepe- December 2015 and March 2016 issues of the American linian view of Kraepelin and argue that the true, histori- Journal of Psychiatry contain a debate focusing on the cal Kraepelin was far more inclined towards scientific legacy of Emil Kraepelin, widely considered one of the psychology, less reductionist and brain-centric, and more founders if not the iconic founder of modern scientific skeptical nosologically than his later followers apparently psychiatry. The authors, Eric J. Engstrom and Kenneth S. believe. Subsequently, commenting upon Engstrom’s Kendler, challenge the so-called neo-Kraepelinian view and Kendler’s paper, Rael D. Strous, Annette A. Opler of Kraepelin and argue that the true, historical Kraepelin and Lewis A. Opler do not question these claims per se, was far more inclined towards scientific psychology, but rather recall and emphasize historical facts that the less reductionist and brain-centric, and more skeptical paper regrettably omitted (2), namely, that Kraepelin nosologically than his later followers apparently believe.
    [Show full text]
  • Lessons from Eugenic History Reforming Zeal of the Government
    _300-----------(QRRESPQNDENCE----N-AT_u_RE_v_oL_.3_37_z6_JA_Nu_A_Rv_I9_s9 entirely on the soil, it has succumbed to the new style of New Zealand life and the Lessons from eugenic history reforming zeal of the government. SIR-Among the four papers on schizo- achieve the sensitivity required to pursue Probably its greatest triumph was the phrenia in the 10 November 1988 issue of this type of research in a manner which is detection of the lack of critical trace Nature, there was one brief reference to in the best interests of human society. elements in volcanic soils, which allowed an early work by the German psychiatric WILLIAM E. SEIDELMAN successful sheep farming over wide geneticist, Professor Ernst Rudin 1.2. North Hamilton Community regions of the North Island; and more Unfortunately, there was no discussion of Health Centre, recently the painstaking investigation of Rudin's work or his career, subjects 554 John Street North, aspects of the Abbotsford landslide painfully relevant to the topic of the Hamilton, Ontario L8L-4Sl, Canada gained the admiration of the geotechnical inheritance of schizophrenia. Rudin was 1. Sherringwn. R .• e1.a/. Na/Ure336. 164-167 (1988). community. an internationally recognized psychiatrist- 2. Rudin. E. Zur Verebung und Neuenlsiehung der Soil science has now been incorporated · · h f" ld f · h Demeflliapraecox. (Springer. Berlin . 191 6). genetiCISt W OSe Ie 0 Interest WaS t e 3. Seidelm an, W.E. Milbank Quanerly. 66. 221- 239 (1988). into the new DSIR Division of Land and genetics of schizophrenia. In 1928, he 4. Stern K. The Pillar of Fire. (Harcourt. Brace, New Soil Science, but the rationalization has became director of the Kaiser-Wilhelm York.
    [Show full text]
  • The Nazi Euthanasia Program: Forerunner of Obama's Death Council
    Click here for Full Issue of EIR Volume 36, Number 24, June 19, 2009 The Nazi Euthanasia Program: Forerunner of Obama’s Death Council by Anton Chaitkin At his trial in front of the American National procedures to be used to deny care to elderly, chroni- Military Tribunal in 1947, Karl Brandt, Hitler’s cally ill, and poor people, whose lives are considered of escort physician and later a leading euthanasia less value. Ezekiel’s brother, Obama’s Chief of Staff operative, testified that, sometime in 1935, Hitler Rahm Emanuel, is ramming this Nazi-revival policy had informed Reich Health Leader Gerhard through Congress. Wagner of his intention to implement euthanasia The President beat the drums on May 11, after meet- of the mentally disabled once war had begun. ing with private insurance companies, saying that be- According to Brandt, Hitler believed the opposi- cause of the financial crisis, $2 trillion must be cut from tion to euthanasia from church circles would be American health-care spending. The companies prom- less pronounced during war than in peacetime. ised to help him shut down more “costly” treatments, —Michael S. Bryant, Confronting the Good Death: which typically prolong life. Nazi Euthanasia on Trial, 1945-1953 (Boulder: University Press of Colorado, 2005) The Nuremberg Precedent * * * In the Medical Case conducted from October 1946 The world economy is teetering . With trillions to August 1947 as part of the Nuremberg War Crimes of dollars evaporating in this crisis, millions of Trials, the United States charged Nazi officials and doc- middle-class Americans face the prospect of tors with mass killing of patients in the euthanasia losing their homes and jobs, and witnessing a (“mercy death”) program.
    [Show full text]
  • Conatus - Journal of Philosophy
    Conatus - Journal of Philosophy Vol. 4, 2019 Eugenics between Darwin’s Εra and the Holocaust Chousou Dimitra University of Ioannina Theodoridou Daniela University of Ioannina Boutlas George National and Kapodistrian University Athens Batistatou Anna University of Ioannina Yapijakis Christos National and Kapodistrian University of Athens Syrrou Maria University of Ioannina https://doi.org/10.12681/cjp.21061 Copyright © 2019 Dimitra Chousou, Daniela Theodoridou, George Boutlas, Anna Batistatou, Christos Yapijakis, Maria Syrrou To cite this article: Chousou, D., Theodoridou, D., Boutlas, G., Batistatou, A., Yapijakis, C., & Syrrou, M. (2019). Eugenics between Darwin’s Εra and the Holocaust. Conatus - Journal of Philosophy, 4(2), 171-204. doi:https://doi.org/10.12681/cjp.21061 http://epublishing.ekt.gr | e-Publisher: EKT | Downloaded at 08/10/2021 21:27:35 | D. Chousou et al. Conatus 4, no. 2 (2019): 171-204 DOI: http://dx.doi.org/10.12681/cjp.21061 Eugenics between Darwin’s Εra and the Holocaust Dimitra Chousou,1 Daniela Theodoridou,2 Georgios Boutlas,3 Anna Batistatou,4 Christos Yapijakis,5 Maria Syrrou6 1University of Ioannina, Greece 2University of Ioannina, Greece E-mail address: [email protected] E-mail address: [email protected] ORCID ID: https://orcid.org/0000-0001-9247-2168 ORCID ID: https://orcid.org/0000-0001-5468-0337 3National and Kapodistrian University of Athens, Greece 4University of Ioannina, Greece E-mail address: [email protected] E-mail address: [email protected] ORCID ID: http://orcid.org/0000-0002-1898-2845 ORCID ID: https://orcid.org/0000-0003-4353-9535 5National and Kapodistrian University of Athens, Greece 6University of Ioannina, Greece E-mail address: [email protected] E-mail address: [email protected] ORCID ID: https://orcid.org/0000-0001-6695-186X ORCID ID: https://orcid.org/0000-0002-5748-5008 Abstract Heredity and reproduction have always been matters of concern.
    [Show full text]
  • (Mather, 1949), and Otherwise Appear to Be Inherited in the Classical Mendelian Fashion
    430 NOTES AND COMMENTS ADEFINITION AND STANDARD NOMENCLATURE FOR "POLYGENIC LOCI" JAMES N. THOMPSON, Jr. and J. M. THODAY Department of Genetics, University of Cambridge, Milton Road, Cambridge CM I Xl-! Received3.vi.74 SUMMARY Studies of qualitative and quantitative or continuous genetic variation are, in part, historically and methodologically separate. But the traditional distinction between major genes and polygenes has unfortunately caused some confusion in discussions of the location of polygenes and the nature of the loci which contribute to quantitative variation. Consequently, this paper proposes that the term "polygeniclocus" replace the term "polygene" when reference is made to the effects of individual loci. A polygenic locus is defined as a genetic locus composed of one or more closely linked genes at which allelic substitutions contribute to the variance in a specified quantitative character. A standard nomenclature is described. 1. INTRODUCTION A CHARACTER shows quantitative or continuous variation when the pheno- type is affected by a number of factors, each of which makes a contribution which is small relative to other sources of variation. When these factors include allelic variation at one or more genetic loci, the other sources of variation, which may be environmental, genetic, or both, make it difficult to classify individual genotypes. Thus, segregation at individual loei cannot be studied directly. On the other hand, a character shows qualitative, discontinuous, or Mendelian variation when genetic variation at one or a very small number of loci makes large individual contributions to pheno- typic variance relative to other genetic and environmental factors. In such a situation, variation in the character allows individuals to be classified into distinct phenotypic classes with the result that the segregation of individual alleles can be easily detected.
    [Show full text]
  • Current Opinions in Neurological Science ISSN: 2575-5447
    Page 53 to 62 Volume 1 • Issue 1 • 2017 Review Article Current Opinions in Neurological Science ISSN: 2575-5447 Medicine and the Third Reich Michael Besser AM* Clinical Associate Professor and Lecturer in Surgical Anatomy, University of Sydney, Australia *Corresponding Author: Michael Besser AM, Clinical Associate Professor and Lecturer in Surgical Anatomy, University of Sydney, Australia. Received: March 17, 2017; Published: May 08, 2017 Abstract In the period leading up to the Second World War, and during the war itself, the medical profession in Germany was instrumental in and cognitively compromised” (Strous, 2006, p30). The role of psychiatric medicine was central and critical to the success of Nazi the institution of a system which identified, transported and killed human beings either mentally ill, physically deformed or “racially ideology rather than marginal or incidental. Psychiatrists played a central and intimate role in the facilitation of crimes against hu- manity. This paper will explore and try to explain some of the complex issues involved in an effort to understand a shameful, tragic interval in medicine. Keywords: Psychiatry; Eugenics; the Holocaust; Medical Ethics Volume 1 Issue 1 May 2017 © All Copy Rights Reserved by Michael Besser AM. Introduction - Dissection of the motives and activities of doctors, especially psychiatrists, as they existed under a regime and in a society labelled as the “banality of evil” (Arendt, 1977, p135), indicates they were a product of a destructive society whose ideology they not only col luded with, but helped mould. Their rationalisations were based on corrupt ethics and faulty scientific theory which applied invalid conclusions from evolutionary biology.
    [Show full text]
  • Kallmann Syndrome: Eugenics and the Man Behind the Eponym
    Open Access Rambam Maimonides Medical Journal MEDICINE AND SOCIETY Kallmann Syndrome: Eugenics and the Man behind the Eponym Carlos A. Benbassat, M.D.1,2* 1Endocrine Institute, Assaf Harofeh Medical Center, Zerifin, Israel; and 2Sackler Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel ABSTRACT Kallmann syndrome is named after Franz Joseph Kallmann, a German-born psychiatrist who described in 1944 twelve subjects from three families who presented with a syndrome of missed puberty, anosmia, and color blindness. Yet, several other eponyms for the same syndrome can be found in the literature. Despite the fact that Kallmann syndrome is the most recognized eponym, very little is known about the man for whom the syndrome is named. A biographical note on Franz Joseph Kallmann and his historical context is presented. KEY WORDS: Eugenics, Kallmann syndrome, Nazi medicine, racial hygiene INTRODUCTION Kallmann syndrome is a congenital disorder of the ever, that Kallmann and colleagues drew attention hypothalamus, characterized by reduced pituitary to the genetic etiology of the disorder in a study of 12 gonadotropic activity resulting in hypogonadism subjects from three families who presented with a with associated anosmia. In 1856, Aureliano syndrome of missed puberty, anosmia, and color Maestre de San Juan described the autopsy findings blindness. Two of them were also mentally retard- in a 40-year-old man with absent olfactory lobes, ed.3 Ten years later, De Morsier documented 14 af- small testicles, small penis, and no pubic hair.1 fected persons and confirmed that the anosmia was Several years later, Richard L. Heschl reported a consequence of agenesis of the olfactory lobes.4 similar findings in a 45-year-old man.
    [Show full text]
  • Extermination of the Jewish Mentally-Ill During the Nazi Era — the “Doubly Cursed”
    Isr J Psychiatry Relat Sci Vol 45 No. 4 (2008) 247–256 Extermination of the Jewish Mentally-Ill during the Nazi Era — The “Doubly Cursed” Rael Strous, MD Beer Yaakov Mental Health Center, Sackler Faculty of Medicine, Tel Aviv University, Ramat Aviv, Israel. Abstract: In Nazi Germany, physicians initiated a program of sterilization and euthanasia directed at the mentally-ill and physically disabled. Relatively little is known regarding the fate of the Jewish mentally-ill. Jewish mentally-ill were definitely included and targeted and were among the first who fell victim. They were systematically murdered follow- ing transfer as a specialized group, as well as killed in the general euthanasia program along with non-Jewish mentally- ill. Their murder constituted an important link between euthanasia and the Final Solution. The targeting of the Jewish mentally-ill was comprised of four processes including public assistance withdrawal, hospital treatment limitations, sterilization and murder. Jewish “patients” became indiscriminate victims not only on the basis of psychiatric diagno- sis, but also on the basis of race. The killing was efficiently coordinated with assembly in collection centers prior to being transferred to their deaths. The process included deceiving Jewish patients’ family members and caregivers in order to extract financial support long after patients had been killed. Jewish patients were targeted since they were helpless and considered the embodiment of evil. Since nobody stood up for the Jews, the Nazis could treat the Jewish patients as they saw fit. Several differences existed between euthanasia of Jews and non-Jews, among which the Jewish mentally-ill were killed regardless of work ability, hospitalization length or illness severity.
    [Show full text]
  • Chapter 15 the Chromosomal Basis of Inheritance
    CHAPTER 15 THE CHROMOSOMAL BASIS OF INHERITANCE OUTLINE I. Relating Mendelism to Chromosomes A. Mendelian inheritance has its physical basis in the behavior of chromosomes during sexual life cycles B. Morgan traced a gene to a specific chromosome: science as a process C. Linked genes tend to be inherited together because they are located on the same chromosome D. Independent assortment of chromosomes and crossing over produce genetic recombinants E. Geneticists can use recombination data to map a chromosome’s genetic loci II. Sex Chromosomes A. The chromosomal basis of sex varies with the organism B. Sex-linked genes have unique patterns of inheritance III. Errors and Exceptions to Chromosomal Inheritance A. Alterations of chromosome number or structure cause some genetic disorders B. The phenotypic effects of some genes depend on whether they were inherited from the mother or father C. Extranuclear genes exhibit a non-Mendelian pattern of inheritance OBJECTIVES After reading this chapter and attending lecture, the student should be able to: 1. Explain how the observations of cytologists and geneticists provided the basis for the chromosome theory of inheritance. 2. Describe the contributions that Thomas Hunt Morgan, Walter Sutton, and A.H. Sturtevant made to current understanding of chromosomal inheritance. 3. Explain why Drosophila melanogaster is a good experimental organism. 4. Define linkage and explain why linkage interferes with independent assortment. 5. Distinguish between parental and recombinant phenotypes. 6. Explain how crossing over can unlink genes. 7. Map a linear sequence of genes on a chromosome using given recombination frequencies from experimental crosses. 8. Explain what additional information cytological maps provide over crossover maps.
    [Show full text]
  • Genetics Applied to Forestry an Introduction
    Genetics Applied to Forestry An Introduction Gösta Eriksson Inger Ekberg David Clapham Genetics Applied to Forestry An Introduction Third edition Gösta Eriksson Inger Ekberg David Clapham ISBN 978-91-576-9187-3 1 © 2013 Gösta Eriksson Inger Ekberg David Clapham ISBN 978-91-576-9187-3 Cover photos. Above: A Pinus sylvestris stand in Distribution Central Sweden, photograph Britt Ekberg-Eriks- Department of Plant Biology and Forest VRQ%HORZ$SURIXVHO\ÀRZHULQJTilia cordata Genetics, SLU, Box 7080, 750 07 Uppsala, Sweden tree in Central Sweden, photograph Inger Ekberg. Contact: [email protected] Printing: Elanders Sverige AB 2 Preface This book is a follow-up of An Introduction to Forest Genetics. It is somewhat expanded compared to the book printed in 2007. We were encouraged to ”publish” the revised version of the textbook on the internet. Undergraduate students are the target group as well as graduate students with limited experience of forest genetics. Without the advice and help from Kjell Lännerholm, Björn Nicander, Johan Samuelsson and Hartmut Weichelt the editing would have been more troublesome. We express our sincere thanks to them. A generous grant from Föreningen Skogsträdsförädling, The Tree Breeding Association in Sweden, made this printing grant from Föreningen Skogsträdsförädling, The Tree Breeding possible. A web version of this book may be found under http://vaxt2.vbsg.slu.se/forgen/Forestry_Genetics.pdf Uppsala December 2013 Gösta Eriksson Inger Ekberg David Clapham 3 Content Chapter 1 Chromosome cytology ................................7
    [Show full text]
  • Genetic Analysis of Resistance of Wild Melon to Podosphaera Xanthii Race 2F
    African Journal of Agricultural Research Vol. 6(14), pp. 3340-3345, 18 July, 2011 Available online at http://www.academicjournals.org/AJAR DOI: 10.5897/AJAR11.487 ISSN 1991-637X ©2011 Academic Journals Full Length Research Paper Genetic analysis of resistance of wild melon to Podosphaera xanthii race 2F Feng Xian, Yong Zhang, Jianxiang Ma, Jianqiang Yang and Xian Zhang* College of Horticulture, Northwest A and F University, Yangling 712100, Shaanxi, China. Accepted 15 June, 2011 Yuntian-930 is a wild melon that is highly resistant to powdery mildew (PM). To determine the inheritance of resistance to PM, Yuntian-930 was crossed with another cultivated melon, Hualaishi, which is susceptible to PM. Inheritance of resistance to Podosphaera xanthii race 2F. in six plant generations (P 1, P 2, F 1, B 1, B 2, and F 2) was studied using the mixed major-gene plus polygene inheritance mode with joint analysis method. Inheritance of resistance in wild melons fitted the model of two pairs of additive-dominance-epistasis major genes plus additive-dominant-epistasis polygene. The additive, dominant and epistatic effects between the two major genes played an important role in inheritance. The estimated values of heritability of major genes in B1, B 2 and F 2 were 62.98, 58.58 and 90.89% and those of polygene heritability were 28.93, 31.47 and 3.22%, respectively. The ratios of the environmental variance to phenotype variance were 5.89 to 9.94%. Thus, resistance of Yuntian-930 to PM was controlled not just by two major genes, but was also affected by polygene and the environment.
    [Show full text]