Horse Genetics. Ernest Bailey

facts and ideas to provide horse breeders with relevant illustrations. While providing a basic primer, I will not oversimplify to the point of inaccuracy. Students and science professionals can confidently use this handbook as a resource.

      Do not expect to read this book from cover to cover! In my years of teaching, I have found that genetics is a subject that can only be taken in small doses. When you reach your saturation point, stop for the moment to return at another time.

      Browse the contents, the pictures and tables to become familiar with the material present. You may want to read only selected chapters or sections. The index may point you to several sections discussing a subject of particular interest. If you wish to read the original research papers, the reference section provides the citations to find them in a university library. You will probably want to have a general genetics textbook at hand to refresh your memory or to provide alternative and more detailed examples of basic principles.

      Knowledge about horse genes lags well behind that for human or mouse, or even for genes of other domestic animals such as cow, pig, sheep, and chicken. Since the horse provides only a very limited set of examples, readers keen to know more about genetics are encouraged to consult current texts in general genetics. I especially recommend the veterinary genetics textbook by Nicholas (1987) [current edition

      Nicholas, F.W. (2010) Introduction to Veterinary Genetics. Wiley-Blackwell, Ames, Iowa] for its wealth of animal examples.

      You may find the contents overwhelmingly detailed about Paint horse pattern genes. The emphasis is a reflection of the many inquiries I receive from Paint breeders. Even if white spotting genes don’t pertain to your breeding program, they provide examples to help you practice thinking about horse genetics. You may be disappointed that no discussion is provided on a particular subject important to your breeding program. Information specific to horse genetics comes at a price. Government-funded agriculture programs support research on food and fiber animals, not companion animals. Knowledge about horse genetics will be forthcoming in direct proportion to how much money is invested. Without money being committed to horse research by horse breeders, our understanding about genetics of humans, mice, and cattle will continue to advance rapidly, but knowledge about horse genetics will only unfold slowly.

      Readers of this book will find answers to many of their questions about the genetics of horses, but I hope that other questions will replace them. Learning is a continuous process that does not end with finding answers. The path of knowledge is learning to ask questions and to build new questions from the answers.

      Ann T. Bowling

      1996

Preface to the Second Edition

      The preface written for the first edition remains pertinent. At the same time many new discoveries have been made since the first edition of this book was written. Ann Bowling wrote the first edition just when molecular genetics was beginning to be applied to horses. At that time, parentage testing was converting from blood typing technologies to DNA technologies. The mutation had been identified for one coat color gene (extension) and one disease gene (hyperkalemic periodic paralysis in Quarter Horses). Scientists were beginning to construct a genetic map for the horse with hopes of making more discoveries. Indeed, a lot has happened during the intervening 18 years. The entire DNA sequence of a Thoroughbred horse was determined. Molecular genetics has been used to identify many color genes and disease genes. Molecular markers have now replaced blood typing markers for parentage testing. DNA information is providing insights on the domestication of horses and the relationships among breeds. We are beginning to identify specific DNA sequences that influence performance and behavior. Many more horses have now had their entire DNA sequence completed. Genetics has become even more interesting and more useful.

      Several years ago, the publishers asked us if we could update the existing text. Initially we declined, responding that so much had happened that it would take more than a revision to produce a useful text. However, when we took a closer look at the book, we were impressed by the organization of the topics and the quality of Ann’s descriptions and explanations.

      We did make some changes. We deleted the chapter on gene mapping and added chapters on evolution and genomics. The organization of the color pattern chapters was changed to reflect insights gleaned from molecular genetics. The book contains a large amount of new information and concepts reflecting research during the last decade. Nevertheless, this book remains a revision inasmuch as the organization is true to Ann’s original plan. Her book was a thoughtful challenge to regard genetic questions as puzzles that could be addressed with a wide range of tools.

      Ann was fascinated with horse genetics and loved the opportunities she was afforded at the University of California, Davis, to work on all aspects of horse genetics, especially coat color and cytogenetics. She was also an enthusiastic leader in gene mapping research up to the time of her passing. Ann passed away on December 8, 2000 as a result of a massive stroke. The stroke was a complete surprise and Ann was at work discussing research with a colleague when it occurred. However, the greater tragedy was the loss endured by her family. Ann was a wife and mother, devoted to her family. She spoke often and proudly of Michael and Lydia. Together they operated an Arabian Horse breeding farm and were proud of their bloodlines and the accomplishments of their produce.

      The spirit of this book reflects Ann’s love of horses and genetics. This book is not necessarily the one she would have written, but Ann contributed to many of the advances described in this book and enjoyed learning of accomplishments by others. We anticipate horse breeders and owners will find the updated text useful. The material in the book includes breeding practices that are products of centuries of experience as well as new information and concepts that will make horsemanship more successful for horse and rider.

      The authors are very grateful to several colleagues for critical reading of chapters especially to Drs Teri Lear and Rebecca Bellone who provided extensive help with the chapters on Cytogenetics and Leopard Spotting. Many colleagues also provided images for this book and are identified in the legends accompanying the images.

      Ernest Bailey

      Samantha A. Brooks

      27 November 2012

Preface to the Third Edition

      Horse genetics has not changed since Ann Bowling wrote the first edition of this book; however, the tools have changed profoundly. The gray coat color allele is still dominant and normal horses still have 32 pairs of chromosomes. Yet, today, the whole genome sequence for the horse is freely available on the internet and we can use molecular genetic tests to reaffirm many of the observations of horse breeders, to refine others and to discover aspects of the horse that we could not imagine.

      The first edition of this book was published when DNA studies were first being applied to the horse. The second edition followed completion of the whole genome sequence of the horse. Now, seven years later, over 2000 horses have had their whole genomes sequenced, DNA tests using ancient horse bones have revolutionized our understanding of horse domestication, and the studies on regulation of gene expression have become the cutting edge of genetics research for the horse.

      We do not need to be molecular geneticists to use this information. We can buy commercial DNA tests for coat color traits and disease susceptibility genes. Therefore, the purpose of this book is to provide basic information on genetics in an easy-to-understand format. As before, the book includes introductory chapters on basic genetics that review terminology and fundamental concepts. At the same time, the text contains very specific information about the DNA variants associated with traits, scientific speculation about how those traits came to be, and advice on how to apply the wide variation occurring among horses. It is not a book to read through at one sitting. The reader may want to simply peruse the table of contents and select sections pertaining to their interests. References are included to the original work if the reader wants details; however, these detailed studies are not necessary for a useful understanding of this new information.

      The book covers a wide range of