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Heredity and Variation L.C. Dunn

Heredity and Variation

L.C. Dunn

Published March 1st 2007
ISBN : 9781406767216
Paperback
132 pages
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Text extracted from opening pages of book: HEREDITY AND VARIATION Continuity and Change in the Living World By L. C. DUNN, D. Sc. PROFESSOR OF ZOOLOGY, COLUMBIA UNIVERSITY Highlights of Modern Knowledge GENETICS THE UNIVERSITY SOCIETY, INC.MoreText extracted from opening pages of book: HEREDITY AND VARIATION Continuity and Change in the Living World By L. C. DUNN, D. Sc. PROFESSOR OF ZOOLOGY, COLUMBIA UNIVERSITY Highlights of Modern Knowledge GENETICS THE UNIVERSITY SOCIETY, INC. Educational Publishers NEW YORK COPYRIGHT, 1932, 1934. BY THE UNIVERSITY SOCIETY INCORPORATED Manufactured in the IT. 8. 1. CONTENTS CHAPTER PAGE I THE SIGNIFICANCE OF HEREDITY 1 The Nature of the Subject Resemblances and Differ ences The Meaning of Heredity and Variation Re semblances Are Never Quite Perfect The Mechanism of Heredity Heredity and Experience Genetics a Fun damental Science Making Use of the Knowledge of Heredity Some of the Problems Life Follows Natural Laws II REPRODUCTION AND HEREDITY 10 Passing of Old Ideas New Ideas and New Discoveries The Continuity of All Life The Importance of This Discovery The Essential Nature of Sexual Reproduction Some Early Clues to the Riddle of Heredity Sex in Plants Expansion of Knowledge Attempts to Find a Solution Mendel and His Work III MENDELS DISCOVERY 19 The Questions at Issue Confirming Mendels Work The Man and His Ideas The Nature and Results of Mendels Discovery The Principles Involved The Facts of Experience Inheritance of Two Characters Combi nations and Ratios u Blending Inheritance Human Character Differences Genes Which Kill The Gene and the Individual IV THE MECHANISM OF HEREDITY 43 Questions to Be Solved The Methods Employed Cell Division The Result and Significance of Cell Division The Nature of the Gametes - Gametes of Plants Prepa ration of the Gametes The Cells and-the Chromo somes The Pairs of Chromosomes The Fly Droso phila The Genes and the Chromosomes Dr. MorgansExperiments Other Discoveries The Genes Stick To gether Explaining Gene Associations-Cross-Overs or Breaks in the Linkage Mapping the Genes The Impor tance of the Gene A New Conception of Life iv CONTENTS CHAPTER PAGE V HEREDITY AND SEX 67 The Problem of Sex Is Sex Hereditary ? The Sex Differ ence Other Functions of the Sex Glands The Chromo somes in the Male and Female When Is Sex Deter mined Some Interesting Proofs Control of Sex Sex Determination in Animals and Plants VI THE ORIGIN OF VARIATIONS 76 Two Vital Questions The Answers to the Questions The Problem of Environment What Are the Facts The Question of Mutilations Inheritance of Effects of Training Effects of Poisons Origin of New Char acters Recombinations of Old Characters The Appear ance of Sports Mutations The Results of Laboratory Observation The Frequency of New Genes What Happens When a New Gene Arises Artificial or Induced Mutations Practical Use of X-ray Mutations Conclusion VII THE APPLICATION OF THE NEW IDEAS 92 Applications to Evolution The Meaning of Natural Selection Knowledge of Heredity Application to Ani mals and Plants Inbreeding and Its Results Hybrid Vigor The Effect of Blood Relationship Obtaining Vigorous Hybrids Marriage Between Cousins Appli cations to Human Society The Need for Eugenics Heredity and Environment What Do We Inherit? SUGGESTIONS FOR FURTHER READING 114 GLOSSARY 115 INDEX 117 HEREDITY AND VARIATION Continuity and Change in the Living World By L. C. DUNN, D. Sc. PROFESSOR OF ZOOLOGY COLUMBIA UNIVERSITY To My Wife THE MONUMENT TO GREGOR MENDEL, FOUNDER OF THE SCIENCE OF GENETICS At Briinn, Czecho-Slovakia, where he carried out his famous experiments CHAPTER I THE SIGNIFICANCE OF HEREDITY THEstudy of a science which deals with the processes by which new living things come into being must be conceded to be fundamental to an understanding of life and its laws. Genetics, the scientific study of heredity and variation, is still a comparatively new subject, but it has already built up a body of principles which are rapidly gaining popular consideration and finding important practical applications. Intelligent people wish to know and need to know the nature of those laws by which heredity operates, not only because the laws themselves are clear and general and well es