This teacher's guide is intended to be used with "Genes and Surroundings," an activity unit on human and medical genetics for junior high and middle school students. The unit emphasizes variability and diversity in genetics and is organized around five themes: (1) individuality; (2) continuity; (3) variability in relation to others; (4) variability in time; and (5) adaptation. The initial section of the teacher's guide provides a list of materials needed for each of the 25 activities, an overview of the unit, recommended administrative arrangements including a letter to parents and a parent permission form, organization and goals of the program, teaching considerations, and evaluation suggestions. Each activity has specific instructions which are divided into eight parts: focus; objectives; additional learning opportunities; materials and advance preparation needed; teaching considerations including instructional methods, background information, and alternative approaches; guide to class discussions; suggestions for further exploration; self-check key; and new words. A test item bank to assist in test development and tear sheets for use with some of the activities are included. (DC)