ABSTRACT
More than 200 genes have been identified as causing hereditary diseases; new genes are isolated at a rate of 1 per month (Singer & Berg, 1997; Thompson, Hellack, Braver, & Durica, 1997). Some childhood disorders originate solely from prenatal or postnatal environmental events (e.g., deaf-blindness in the offspring caused by the pregnant mother contracting rubella, exposure to toxic chemicals such as PCBs [polychlorinated biphenyls], or sustainment of a traumatic head injury) but many are clearly related to a defective gene transmitted through the generations (e.g., albinism, hemophilia, sickle cell anemia, Tay-Sachs). Still other conditions appear to result from genetic susceptibility coupled with prenatal or postnatal stressors (e.g., stuttering, Giles de la Tourette’s syndrome). To facilitate an understanding of genetic conveyance, principles of hereditary transmission are presented and illustrated. A glossary is provided at the end of the chapter to facilitate an understanding of common genetic terms.
