Chromosomal defects are one of the most common causes of genetic disorders and are responsible for a large proportion of miscarriages. As a result, more and more parents are becoming interested in genetic counseling in order to learn about the risks of reproductive failure, or to understand why they had a child with a particular defect, whether it will happen again, and what might be done to prevent it. This book addresses these and other questions concerning chromosome abnormalities. Although the book is written primarily for genetic counselors and laboratory workers in cytogenetics, it will be of interest to all physicians concerned with genetic counseling. Each chapter discusses a different type of defect, such as translocations, duplications, insertions, deletions, and non-disjunction. The basic biological theory underlying the problem is discussed and in-depth information is provided on the reproductive risks of chromosomally abnormal individuals and of normal parents who have a child with a chromosome abnormality. The book will help concerned parents determine an appropriate course of action, including prenatal diagnosis, and help counselors to communicate the information necessary for responsible decision-making.