DOCSLIB.ORG

Erwin Baur Or Carl Correns: Who Really Created the Theory of Plastid Inheritance?

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Erwin Baur Or Carl Correns: Who Really Created the Theory of Plastid Inheritance? Erwin Baur or Carl Correns: Who Really Created the Theory of Plastid Inheritance? Rudolf Hagemann Historical reviews of the field of non-Mendelian genetics and many other publica- tions credit Erwin Baur and Carl Correns equally for the development of the theory of plastid inheritance. However, a study of the original literature indicates that this conclusion is not correct. Analysis of the relevant articles leads to the conclusion that Baur alone deserves credit for the theory of plastid inheritance. In his classic article on the inheritance properties of white-margined Pelargonium plants, Baur (1909) stated: (1) The plastids are carriers of hereditary factors which are able to mutate. (2) In variegated plants, random sorting-out of plastids is taking place. (3) The genetic results indicate a biparental inheritance of plastids by egg cells and sperm cells in Pelargonium. By contrast, Correns held the view that in variegated plants there is a maternally transmitted labile state of the cytoplasm which switches either to a permanently ‘‘healthy’’ state (allowing the ‘‘indifferent’’ plastids to be- come green chloroplasts) or to a permanently ‘‘diseased, ill’’ cytoplasmic state (causing white plastids and cells). Otto Renner supported Baur’s theory and worked out important characteristics of plastid inheritance in the genus Oenothera. In the 1930s Renner reported many more observations, which established plastid inher- itance as a widely accepted genetic theory. Plastid Genetics as an Integral basic research, plastids have also attract- Part of Current Genetic Research ed the attention of plant biotechnologists due to the recent development of trans- Research involving plastid as well as mi- formation technologies for higher plant tochondrial genetics has contributed to chloroplasts, which enable the expression recent advances in both basic and applied of foreign genes in the plastid compart- research. Over the past 15 years the com- ment (Bock and Hagemann 2000). plete DNA sequences of several plastid ge- In contrast to the general importance of nomes from higher and lower plants have research on plastid genetics, many text- been determined. In addition, extensive books of genetics (irrespective of their studies on the expression of plastid genes, country of origin) almost completely ig- their mutations, their regulation, and in- nore the field of plastid genetics: it is men- teraction with the nucleocytoplasmic tioned on at most two or three pages in a compartment have advanced our knowl- total text of 500 or 800 pages and, more- edge of the role of plastid genes within the over, the text frequently contains errone- genetic system of plants. ous statements. (The situation regarding Recent molecular work also has provid- mitochondrial genetics is slightly—but ed new insights into the evolution of plas- not much—better.) tids from formerly free-living cyanobacte- This article addresses this problem by ria. Nowadays a wealth of genetic, providing a review of the original litera- biochemical, and cytological data support ture from the turn of the 20th century. the idea that the endosymbiotic uptake of This summary of the German literature a cyanobacterium by a pre-eukaryotic cell may also be useful to scientists within the From the Institute of Genetics, Martin-Luther-Universi- ty, Weinbergweg 10, D-06099 Halle/Saale, Germany. I was followed by the gradual transforma- discipline of organelle genetics who have wish to thank Dr. Ralph Bock for valuable discussions tion of the endosymbiont into a plastidlike questions concerning the history of this of the manuscript and his advice for improvement of cell organelle—a process accompanied by field, how this discipline has evolved from the text. Moreover, I thank Dr. Richard Tilney-Bassett and three anonymous referees for critical reading of massive gene transfer from the plastid ge- its very beginning, and who was the dis- the manuscript and many valuable comments. nome to the chromosomes in the cell nu- coverer of the basic principles of plastid ᭧ 2000 The American Genetic Association 91:435–440 cleus. In addition to their importance in inheritance. 435 Discovery of Non-Mendelian green versus white. The F1 progeny con- (Extranuclear) Inheritance by Carl sisted of green, green-white variegated, Correns and Erwin Baur and white seedlings. In many crosses there was a bias in the F toward the phe- In one issue (no. 3) of Volume 1 of the 1 notype of the maternal parent. ‘‘Zeitschrift fu¨r induktive Abstammungs- Thus, in 1909, Baur and Correns simul- und Vererbungslehre’’ (the first interna- taneously discovered and described the tional journal of genetics and the progen- occurrence of non-Mendelian inheritance itor of Molecular and General Genetics), in higher plants. Their conclusion that in Correns and Baur separately published ar- addition to the Mendelian inheritance of ticles on non-Mendelian inheritance of var- genes in the cell nucleus, there are other iegated phenotypes in plants. Correns hereditary factors outside the nucleus (1909a) emphasized in a footnote to his (i.e., in the protoplasm) which exhibit a article: ‘‘The simultaneous publication of non-Mendelian mode of inheritance marks this paper with the following article by E. a milestone in genetics and the date of Baur is based on mutual agreement; how- birth for a new field of research. Although ever, each of us had no knowledge of the credit for the initial observations should contents of the other ones paper.’’ The ti- be shared between Baur and Correns, tles of the two articles are their subsequent theoretical interpreta- Correns, Carl. Vererbungsversuche mit tions distinguish their contributions to the Figure 1. Erwin Baur (1875–1933). blass(gelb)gru¨nen und buntbla¨ttrigen Sip- field. pen bei Mirabilis jalapa, Urtica pilulifera und Lunaria annua. Zeitschr f ind Abst u (from the other parent). In the course of The Foundation of the Theory of Vererbungsl 1909;1:291–329. (Inheritance the subsequent cell divisions, plastids seg- Plastid Inheritance experiments with pale (yellow) green and regate randomly. This random segregation variegated varieties of Mirabilis jalapa, Ur- The authors of numerous monographs, re- regularly results in sorting out of the two tica pilulifera and Lunaria annua.) view articles, and textbooks express the types of plastids and—during ontogenetic opinion that, in 1909, Erwin Baur and Carl growth of the plants—in the formation of Baur, Erwin. Das Wesen und die Erbli- Correns contributed equally to the estab- pure green and pure white areas in one chkeitsverha¨ltnisse der ‘‘Varietates albom- lishment of the theory of plastid inheritance. and the same plant. arginatae hort.’’ von Pelargonium zonale. However, a careful study of the original lit- Baur’s development of this theory is Zeitschr f ind Abst u Vererbungsl 1909;1: erature indicates that this interpretation documented by the following citations 330–351. (The nature and the inheritance does not reflect the history of plastid genet- from his 1909 paper (in English transla- properties of horticultural varieties of Pel- ics correctly. Below, the original sources in tion): argonium zonale having white borders.) the genetic literature are analyzed. For different plant species both authors I have, on the basis of these observations, reported the non-Mendelian mode of in- The Position of Erwin Baur formed a theory which shall serve as a working hypothesis for the following investigations [. .] heritance of green-white or green-yellow The theory of plastid inheritance and of ran- The P. zonale races with white-margined leaves leaf variegations. dom sorting out of plastids. In his article are chimeras with a periclinally divided growing Following crosses between variegated, Baur (1909) was the first to provide the point.. The peripheral two or three cell layers yellow, and green plants (or branches) of explanation that chloroplast defects in P. of the shoot apex have only albino plastids, which entirely lack the capacity of chlorophyll Mirabilis, Urtica, and Lunaria, Correns zonale and their mode of inheritance are formation. The central cells of the shoot apex, found that the leaf color trait (green ver- cases of plastid inheritance: The green however, contain entirely normal plastids ca- sus yellow) is inherited through the moth- and the white shoots of variegated plants pable of turning green. er only, that is, that there is a purely ma- differ in the genetic constitution of their The fertilized egg cell, as generated through ternal inheritance: green branches always plastids (Baur used the term ‘‘chromato- the union of a ‘green’ with a ‘white’ gamete cell, thus contains two types of plastids, green and produced seeds that gave rise to green phores’’). One plastid type is green (nor- white. During the cell divisions leading from the seedlings, seeds from yellow branches mal, nonmutated, capable of becoming egg cell to the embryo, the plastids are distrib- yielded only yellow offspring, while the green during ontogenetic development); uted to the daughter cells entirely randomly. variegated branches produced green, yel- the other type is white (mutated, incapa- Whenever a daughter cell receives only white plastids, this cell subsequently will have only low, and green-yellow variegated seedlings ble of becoming green). white descendent cells, and will give rise to a in widely varying ratios. In contrast, the In his 1909 paper, Erwin Baur (Figure 1) white sector within the mosaic; whenever a pollen-providing parent had no influence explained the green-white variegation of daughter cell receives only green plastids, a sol- on the phenotype of the progeny. seedlings and the formation of branches in id green sector will arise from it. Cells with both Baur found another type of non-Mende- the F plants with different phenotypes types of plastids will be capable of segregating 1 further, and so on.; probably, I need not explain lian inheritance in his crossing experi- (green, variegated, white; periclinal or sec- this in greater detail. If the cell, which will give ments with P.
Load more

Recommended publications
  • The Hereditary Statistics of Hugo De Vries
    Acta Bot. Neerl. 47(4), December 1998, p. 427—463 The Hereditary Statistics of Hugo de Vries Erik Zevenhuizen Institute for Systematics and Population Biology, Faculty of Biology, University of Amsterdam, Kruislaan 318, 1098 SM Amsterdam, The Netherlands CONTENTS Introduction 427 The theory of pangenesis 429 The use of statistics 432 The laws of chance 435 The Veronica-note: the 5/16-law 439 The Veronica-note: the 1.2.1-law 446 The Aster-note 449 Conclusion: in search of the laws of nature 452 Keywords: Hugo de Vries, Mendel’s laws, mutation theory, pangenesis. INTRODUCTION de Vries is remembered the first of three botanists in Today, Hugo chiefly as who, 1900, publicly announced that they had discovered what we now call the laws of Mendel. All three maintainedthat they had foundthe laws on their own and that, at the moment they did their discovery, they had been completely unaware of the fact that the Austrian amateur botanist Gregor Mendel (1822-1884) had published similar conclusions already in 1866. Whereas his contributions to the development of evolutionary thought are De Vries is credited in generally unappreciated or simply unknown, many surveys on the history of genetics for his rediscovery of Mendel’s laws. It is generally accepted that, together with his two fellow-rediscoverers, Carl Correns from Tubingen and Erich von Tschermak-Seysenegg from Vienna, De Vries made these basic rules of genetics scientific widely known to the world. The year 1900 can be considered as the year of birth of modern genetics, and Hugo de Vries as one of the founders of the discipline.
    [Show full text]
  • Darwin's Influence on Mendel: Evidence from a New Translation Of
    | PERSPECTIVES Darwin’sInfluence on Mendel: Evidence from a New Translation of Mendel’s Paper Daniel J. Fairbanks*,1 and Scott Abbott† *Department of Biology and †Department of Integrated Studies, Utah Valley University, Orem, Utah 84058 ORCID ID: 0000-0001-7422-0549 (D.J.F.) ABSTRACT Gregor Mendel’s classic paper, Versuche über Pflanzen-Hybriden (Experiments on Plant Hybrids), was published in 1866, hence 2016 is its sesquicentennial. Mendel completed his experiments in 1863 and shortly thereafter began compiling the results and writing his paper, which he presented in meetings of the Natural Science Society in Brünn in February and March of 1865. Mendel owned a personal copy of Darwin’s Origin of Species, a German translation published in 1863, and it contains his marginalia. Its publication date indicates that Mendel’s study of Darwin’s book could have had no influence while he was conducting his experiments but its publication date coincided with the period of time when he was preparing his paper, making it possible that Darwin’s writings influenced Mendel’s interpretations and theory. Based on this premise, we prepared a Darwinized English translation of Mendel’s paper by comparing German terms Mendel employed with the same terms in the German translation of Origin of Species in his possession, then using Darwin’s counterpart English words and phrases as much as possible in our translation. We found a substantially higher use of these terms in the final two (10th and 11th) sections of Mendel’s paper, particularly in one key paragraph, where Mendel reflects on evolutionary issues, providing strong evidence of Darwin’sinfluence on Mendel.
    [Show full text]
  • Tutorial: Mendelian Genetics
    Mendelian Genetics Contents Introduction ........................................................................................................................ 1 Heredity Before Mendel ..................................................................................................... 2 Mendel and the Laws of Heredity....................................................................................... 4 The “Rediscovery” of Mendel ............................................................................................. 7 The Misuse of Mendel ........................................................................................................ 8 Mendel in the Modern World ........................................................................................... 10 References and Resources ................................................................................................ 10 Supplemental Material ..................................................................................................... 11 Introduction Today, when the word “genetics” is mentioned the mind is at once occupied with terms like cloning, PCR, the genome project, and genomics. Just a few decades ago, however, the word genetics conjured up a very different set of terms including crossing, segregation, Punnett square, and binomial expansion. It is not that these terms have disappeared or have been replaced since, it is, rather, that genetics moved full force into the molecular era in the late 1970s and, in the beginning of the twenty-first century,
    [Show full text]
  • The Full Breadth of Mendel's Genetics
    | PERSPECTIVES The Full Breadth of Mendel’s Genetics Peter J. van Dijk*,1 and T. H. Noel Ellis *Keygene N.V., 6708 PW Wageningen, The Netherlands ABSTRACT Gregor Mendel’s “Experiments on Plant Hybrids” (1865/1866), published 150 years ago, is without doubt one of the most brilliant works in biology. Curiously, Mendel’s later studies on Hieracium (hawkweed) are usually seen as a frustrating failure, because it is assumed that they were intended to confirm the segregation ratios he found in Pisum. Had this been his intention, such a confirmation would have failed, since, unknown to Mendel, Hieracium species mostly reproduce by means of clonal seeds (apomixis). Here we show that this assumption arises from a misunderstanding that could be explained by a missing page in Mendel’s first letter to Carl Nägeli. Mendel’s writings clearly indicate his interest in “constant hybrids,” hybrids which do not segregate, and which were “essentially different” from “variable hybrids” such as in Pisum.AfterthePisum studies, Mendel worked mainly on Hieracium for 7 years where he found constant hybrids and some great surprises. He also continued to explore variable hybrids; both variable and constant hybrids were of interest to Mendel with respect to inheritance and to species evolution. Mendel considered that their similarities and differences might provide deep insights and that their differing behaviors were “individual manifestations of a higher more fundamental law.” KEYWORDS Gregor Mendel; genetics; Hieracium; constant hybrids; apomixis The publication of Mendel’s letters to Carl Nägeli by several fertile hybrids will bloom for the first time. They Correns in 1905 was a service to genetics which seems not should be very numerous and I only hope that they repay to have been fully appreciated by most of those who have since the yearning [Sehnsucht!] with which I await them with ’ written accounts of Mendel slifeandwork(MannLesley much information concerning their life histories.” (quoted 1927).
    [Show full text]
  • Gregor J. Mendel – Genetics Founding Father
    Review Czech J. Genet. Plant Breed., 50, 2014 (2): 43–51 Gregor J. Mendel – Genetics Founding Father Erik SCHWARZBACH 1, Petr SMÝKAL2, Ondřej DOSTÁL3, Michaela JARKOVSKÁ3 and Simona VALOVÁ4 1Miroslav, Czech Republic; 2Faculty of Science, Palacký University Olomouc, Olomouc, Czech Republic; 3Mendel Museum and 4Faculty of Science, Masaryk University, Brno, Czech Republic Abstract Schwarzbach E., Smýkal P., Dostál O., Jarkovská M., Valová S. (2014): Gregor J. Mendel – genetics found- ing father. Czech. J. Genet. Plant Breed., 50: 43–51. Mendel’s impact on science is overwhelming. Although based on the number of scientific papers he published he might be considered a meteorologist, his most significant contribution is his study of plant hybrids. This single work puts Mendel on a par with Darwin’s evolutionary theory and establishes him firmly in the frame of today’s biology. The aim of this article is to introduce the personality of Gregor Johann Mendel, focussing not just on his scientific work, but also on his background and what or who influenced him. To understand Mendel’s use of quantification and mathematical analysis of obtained results, representing a radical departure from methods of his predecessors, it is important to know something about their arguments, beliefs, and practices. He designed his experiments to answer a long standing question of hybridization, not inheritance as we perceive it today, since the science of genetics was born considerably later. He studied many genera of plants, but his famous research was on garden peas. To choose a single species for his crosses was fundamental to his success, but also fuelled most of criticism at the time he presented his results.
    [Show full text]
  • Key Genetics Problems and Chi Square
    The Chi-square Test and Genetics 1. In fruit flies (Drosophila melanogaster), wild type flies are normal looking and have no obvious mutations. Wild type traits tend to be dominant to many of the mutations that affect fruit flies. One recessive mutation in particular causes a fly to be born with white eyes. In 1910, Thomas Hunt Morgan noticed a white-eyed male fly in his experimental fly population. He bred this fly to several wild type females and 1,237 flies were produced in the F1 generation. Male and female flies were roughly in equal proportions, and all flies had normal red eyes. Morgan then allowed the F1 to mate with each other to produce the F2 generation. The F2 generation had mostly red-eyed flies, and some white-eyed flies, but all the white-eyes flies were males. a. Use Punnett squares to show how the white eye mutation was being passed on in the flies. b. A student performed these crosses and, in the F2 generation, counted 824 flies with the wild phenotype (red eyes) and 297 flies with the white eye phenotype. Perform a Chi- square test to test the null hypothesis (H0) that the observed result of the crosses is statistically indistinguishable from the expected result. Category Observed Expected Expected (O-E)2/E proportion Red eyed 824 3/4 840.75 0.33 White eyed 297 1/4 280.25 1.01 Total 1121 S c2 = 1.34 The critical value for 2 categories at 0.05 is 3.84. Because 1.34 is less than this, the student accepts the null hypothesis (H0) that there is no statistically significant difference between the observed and expected result.
    [Show full text]
  • 15/24/56 Liberal Arts and Sciences Genetics and Development
    15/24/56 Liberal Arts and Sciences Genetics and Development Department Natural History Museum Iltis Mendelania Collection, 1841-1984 Item No Held Description Box Transfer lists: a) “Gregor Mendel Museum, Fredericksburg, 1 Virgina Shelf List” (original ribbon-copy typescript inventory of Iltis’ Mendel Collection, with pencil, pen, and marker annotations presumably added by the Natural History Museum). b) handwritten list (8 pages) of original Mendel “relics” and other Mendel-related items as prepared by the Natural History Museum some time after the 1961 acquisition of the Mendel clock. c) spreadsheet inventory prepared by the University Archives on its acquisition of the collection in 2005 1 Mendel’s birth place in Heinzendorf, Silesia [caption only] 1 The parents consent for Mendel to be priest 2 T 1 Photographic facsimile Mendel’s sisters and his brother-in-law 3 T 1 Photograph and caption Pedigree of Johann Gregor Mendel 4 T 5 Display Board, Hugo Iltis and Jo Anne Campbell 5 T The Common Ancestors of Mendel and Mrs. Hugo Iltis 1 Gregor Mendel’s home country 6 T 5 Display Board The monastery and the church in Altbrünn 7 T 5 Photograph, negative, and caption The convent hall of the monastery, Brünn 8 T 1 Photograph, negative, and caption Mendel’s autobiography, 9 T 7 Photograph of manuscript of last page Autobiography 10 T 5 Photograph of third page Brünn, Spielberg and Franzensberg 11 T 1 Photograph, negative, and caption Gregor Mendel, oil portrait by J.O. Flatter, London, 12 T UAR 49-1 Negative in Box 1 Professor Portrait (“life size”) 13 T 7 Retouched photograph The “handsome” portrait 14 T 5 Photographs and negative T The members of the convent of the Augustines, Brünn 1862 1 15 Caption only.
    [Show full text]
  • The Mendelian and Non-Mendelian Origins of Genetics
    The Mendelian and Non-Mendelian Origins of Genetics Sander Gliboff * Abstract: The story of Gregor Mendel’s long neglect and rediscovery has been criticized for taking Mendel’s paper out of context, both in 1865, when he presented it to the Naturalists’ Society in Brno, and in 1900, when it became a cornerstone of genetics. But what are the proper contexts? Here a case is made for reading Mendel’s paper, in both time periods, as part of a large body of nineteenth-century literature on practical plant- and animal breeding and experimental hybridization. This literature contained a confus- ing and contradictory assortment of observations on heredity and prelimi- nary laws and generalizations, some in line with Mendel’s, but most not. In 1865, Mendel’s paper was intended as a modest attempt to begin to bring order to this chaos, but there was little reason to celebrate it as a break- through: too many “non-Mendelian” cases were known. After 1900, this literature was, in a sense, rediscovered along with Mendel, and it then played a dual role. For critics like W.F.R. Weldon, the non-Mendelian cases falsified Mendel’s laws. But for Mendel’s three co-rediscoverers, William Bateson, and others, they represented challenges to be met within a research program that would modify and extend Mendel’s system and establish a new scientific discipline. Key-words: history of genetics; Mendel, Gregor; rediscovery of Mendel; Bateson, William; Weldon, W. F. R; de Vries, Hugo; Correns, Carl; Tschermak, Erich; plant breeding; hybridization As origens mendelianas e não-mendelianas da Genética Resumo: A história da longa negligência e redescoberta de Gregor Mendel tem sido criticada por tirar Mendel de seu contexto, tanto em 1865, quando * Department of History and Philosophy of Science, Indiana University.
    [Show full text]
  • Nuclear Power Another Way, by Finding Evidence for Dr Sapp Attributes This to the Different I.R.S
    _N_A_TU_R_E__ vo_L_._3_31_J_s_FE_B_R_u_A_R_Y_1_9s_s __________________ 800KREVIEVVS---------------------------------------s7_3 undermine the chromosomal monopoly in heredity received scant consideration. Nuclear power another way, by finding evidence for Dr Sapp attributes this to the different I.R.S. Fincham genetic determinants in the cytoplasm. styles of science administration in the two Dr Jan Sapp's history of these doubts countries; the American 'free market' and disputes makes interesting and pro­ pulled research into the most readily Beyond the Gene: Cytoplasmic Inheritance vocative reading. The interest comes exploitable areas, whereas in the more and the Struggle for Authority in Genetics. largely from extensive and well-selected professorially directed German system By Jan Sapp. Oxford University Press: quotations from the publications and (in founder effects were of more importance. 1987. Pp.266. $35, £32.50. some cases) the personal correspondence According to Dr Sapp, the American of some of the main protagonists. The verdict on the German work was "not GENETICISTS have always tended to believe provocation, at least for this reviewer, proven". But his quotations from Ameri­ that organisms are determined by genes comes from the author's determination to can textbooks of the period show a gen­ located on chromosomes in the cell explain the development of genetics in eral, if tentative, acceptance of a role nucleus. Until the advent of gene cloning, terms of struggles for authority and power for plastids in heredity, an acceptance this belief depended entirely on the between a Mendelian orthodoxy and encouraged, as he points out, by the fact Mendelian behaviour of nearly all varia­ cytoplasmic heresy. that they were visible structures with tion that could be inherited through sexual The three central chapters are mainly apparent continuity through cell division.
    [Show full text]
  • Extranuclear Inheritance
    Extranuclear Inheritance fatchiyah.lecture.ub.ac.id Terms Defined Cytoplasmic inheritance- Transmission of heredity traits through factors in the cytoplasm. Uniparental inheritance- Transmission of heredity traits through only one parent. •maternal inheritance- Uniparental transmission of heredity traits through the mother. •paternal inheritance- Uniparental transmission of heredity traits through the father. „ Extranuclear inheritance refers to inheritance patterns involving genetic material outside the nucleus „ The two most mportant examples are due to genetic material within organelles Mitochondria and chloroplasts „ These organelles are found in the cytoplasm „ Therefore, extranuclear inheritance is also termed cytoplasmic inheritance EXTRANUCLEAR INHERITANCE Mendelian inheritance patterns involve genes that Directly influence the outcome of an organism’s traits and Obey Mendel’s laws Most genes in eukaryotic species follow a Mendelian pattern of inheritance However, there are many that don’t Indeed, linkage which we considered in the last two lectures follows non-Mendelian inheritance Additional patterns of inheritance that deviate from a Mendelian pattern include: Maternal effect and epigenetic inheritance Involve genes in the nucleus Extranuclear inheritance Involves genes in organelles other than the nucleus 1. Mitochondria 2. Chloroplasts 3. plasmid Maternal effect refers to an inheritance pattern for certain nuclear genes in which the genotype of the mother directly determines the phenotype of her offspring
    [Show full text]
  • Chromosomal Theory of Inheritance Long Before Chromosomes Were
    Course Code-EDU161 and Course Name:Botany Chromosomal Theory of Inheritance Long before chromosomes were visualized under a microscope, the father of modern genetics, Gregor Mendel, began studying heredity in 1843. With the improvement of microscopic techniques during the late 1800s, cell biologists could stain and visualize subcellular structures with dyes and observe their actions during cell division and meiosis. With each mitotic division, chromosomes replicated, condensed from an amorphous (no constant shape) nuclear mass into distinct X-shaped bodies (pairs of identical sister chromatids), and migrated to separate cellular poles. Chromosomal Theory Of Inheritance The speculation that chromosomes might be the key to understanding heredity led several scientists to examine Mendel‘s publications and re-evaluate his model in terms of the behavior of chromosomes during mitosis and meiosis. In 1902, Theodor Boveri observed that proper embryonic development of sea urchins does not occur unless chromosomes are present. That same year, Walter Sutton observed the separation of chromosomes into daughter cells during meiosis (Figure). Together, these observations led to the development of the Chromosomal Theory of Inheritance, which identified chromosomes as the genetic material responsible for Mendelian inheritance. (a) Walter Sutton and (b) Theodor Boveri are credited with developing the Chromosomal Theory of Inheritance, which states that chromosomes carry the unit of heredity (genes). The Chromosomal Theory of Inheritance was consistent with Mendel‘s laws and was supported by the following observations: During meiosis, homologous chromosome pairs migrate as discrete structures that are independent of other chromosome pairs. The sorting of chromosomes from each homologous pair into pre-gametes appears to be random.
    [Show full text]
  • Exemplarising the Origin of a Science
    Exemplarising the Origin of a Science A Path to Genetics: From Mendel to Bateson Yafeng Shan Doctor of Philosophy University College London I, Yafeng Shan, confirm that the work presented in this thesis is my own. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. 2 Acknowledgement First of all, I would like to thank my primary supervisor, Emma Tobin, without whom the thesis may have never been close to completion. It has been a great fortune to work under Emma’s supervision in the past three years, not only as a PhD student, but also as a teaching assistant. I benefit so much from her insightful and helpful comments on my thesis writing, as well as her support and advice on my academic life. For me, Emma is much more than a PhD supervisor. I am also extremely grateful to my secondary supervisor, Brendan Clarke, for his critical comments on my writings and useful advice on my job application during the different stages, especially for his suggestion, which encouraged me to look for a case study from the history of biology. I have a great time at UCL, especially STS department. I owe a lot to the support of the STS community, including my PhD colleagues, faculty members, and honourary fellows. I also benefit enormously from the discussions in the reading groups held around UCL, especially the Metaphysical and Scientific Club and the Centre on History of Evolutionary Studies. Special thanks to Jon Agar, Chiara Ambrosio, Jonathan Everett, Toby Friend, Andy Gregory, Andy Hammond, Frank James, Julia Sanchez-Dorado, and Noberto Serpente.
    [Show full text]