INTRODUCTION Human interest in heredity predates modern scientific understanding of genetics. For instance, speculation as to why children do (or sometimes donÊt) resemble their parents may be as old as humanity, and the practice of deliberately breeding plants or animals in order to produce desired char- acteristics was common long before anyone knew the process by which characteristics were passed from parent to child. Efforts to study the rela- tionship between heredity and illness, such as the use of family histories to study patterns of disease among people who were closely related, also predate modern knowledge of genetics. Specific lab tests for genetic and chromosomal diseases started to appear in the mid-20th century, such as the newborn blood test for PKU (phenylketonuria). In the 1970s, lab tests were developed to identify the genetic characteristics associated with Tay- Sachs disease and sickle cell anemia. Today thousands of lab tests are available for different diseases and conditions, and tests are also available to identify some mutations that affect how individual patients may react to certain medicines. While genetic testing is an important tool of modern medicine, the sheer number of tests available can seem overwhelming. While Genetic Testing is not meant to replace professional medical or genetic advice, it does explain the fundamentals of genetics in laymanÊs terms and dis- cusses many of the most common tests and conditions for which tests are available. Need for this kind of guide has increased with the advent of direct-to-consumer (DTC) companies that allow people to order genetic testing outside the context of medical care. This need is particularly great in the United States, where DTC companies are allowed to test for genetic
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