The Search for Human Chromosomes

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1 The Search for Human Chromosomes

2 ThiS is a FM Blank Page

3 Wilson John Wall The Search for Human Chromosomes A History of Discovery

4 Wilson John Wall Bewdley United Kingdom ISBN ISBN (ebook) DOI / Library of Congress Control Number: Springer Cham Heidelberg New York Dordrecht London # Springer International Publishing Switzerland 2016 This work is subject to copyright. All rights are reserved by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, express or implied, with respect to the material contained herein or for any errors or omissions that may have been made. Printed on acid-free paper Springer International Publishing AG Switzerland is part of Springer Science+Business Media (

5 Introduction Why do we need to know how many chromosomes there are in a cell. What are chromosomes made of and how can their behaviour have far-reaching effects on inheritance and health? Simply put why are they so important and why should we all know about them? There comes a point in the curiosity of man when simple observation and description is not enough. This was the point at which genetics was born from observations of plant and animal breeding. The problem of most breeding is that to a casual observer it seems to produce random results, which can then be refined by inbreeding. More than that, some species have a distinct propensity to remain unchained by breeding, whereas species such as dogs can be changed out of all proportion by breeding. This variation in levels of plasticity of the genome in some species gives rise to far greater variation between breeds than in species that do not seem to change to such a large degree. Some species are reluctant producers of varieties for different reasons, for example, large and long-lived trees are not good experimental organisms because they will most likely outlive their researcher before any useful changes can be observed. It may also be that there may not be any reason for a breeder to cast an eye on an already useful and naturally regenerating species. We all know that the coming of the human genome mapping project was seminal in the development of our perception of ourselves, but what most don t realize is that a far more technical and intellectually demanding process takes place in genetic laboratories around the world every day. This is the counting and quantifying of chromosomes. You see, we know that normal human body cells, nonreproductive cells other than red blood cells, all have a complement of 46 chromosomes, but within that is a world of control and expression which depends not just on that number but also on how the material is distributed amongst the chromosomes. Some chromosomes can swap material between them without problem, and some can stick together and cause no trouble for the individual, but may cause untold damage to future generations. Much of this we can now detect and advise on, some can only be detected when the damage has started, as in some cancers as not all tumour-causing damage is due solely to single gene mutations. Chromosomes are complicated. We are looking at the similarity between having a dictionary and saying all the words are there it must be the complete works of Shakespeare. The words have to be in the right order, sentences have to be started and stopped at the v

6 vi Introduction right points, and the players must know their marks. Knowing the human genome is as nothing to knowing how chromosomes structure and control the genome, allowing levels of expression as appropriate in different tissues. All the knowledge which we have about chromosomes and their importance started with the understanding of three things: the first is that they are constant in number, the second is that they are complex structures, and the third is that these are the carriers of the genes. It is surprising that the second and third of these were quickly understood, while the first that they are constant was realized, but the number was for a long time tantalizingly out of reach. In fact for many years, the human chromosome number was erroneously thought to be 48, rather than the true 46. Actually, we glibly say it is 46, but this is really the modal number as cells in culture regularly loose chromosomes. This is not so strange as a cell in culture does not need anywhere the full complement of genes that a tissue or complete organism does. We know that a chromosome carries all the genes, but it is more than that; there is a way in which the chromosomes carry genes, but only in the same way that sleepers carry railway track. They are an integral part of the structure. Without the sleepers the track is just steel; without the genes the chromosome is just a mixture of protein and associated chemicals. At the same time, from a philosophical point of view, the genes are the content, the nebulous part of the chromosome which has no solid existence until they are transcribed into their functional products. The genes on a chromosome are no more than the water molecules in a wave until the wave hits the shore and throws flotsam onto dry land. Bewdley Wilson John Wall

7 Contents 1 Background to the Hunt for the Human Chromosome Number Microscopes and Stains: The Rise of Technology Mendel and Genetics Chromosomes as the Carriers of Heredity Difficulties of Chromosome Handling and Access to Material The Implications of DNA Structure Tissue Culture and the Cell Cycle: The Answer Is Revealed The Flowering of Clinical Genetics Sex and Chromosomes What We Know, What We Don t and Where This May Lead Us Appendix A Rough Guide to Chromosome Structure Appendix B People in the Text Glossary Further Reading vii