Behavioral Genetics An introduction to how genes and environments interact through development to shape differences in mood, personality, and intelligence BY CATHERINE BAKER A tool to inform public discussion of behavioral genetic research and its broader social implications Prepared for a project conducted by the American Association for the Advancement of Science and The Hastings Center For Carolyn, my genetic equivalent Printed in the United States of America Additional copies of this report are available from: ISBN 0-87168-697-X AAAS Scientific Freedom, Responsibility and Law Program Copyright 2004 1200 New York Avenue, NW American Association for the Washington, D.C. 20005, USA Advancement of Science Telephone: USA +1-202-326-6606 Directorate for Science & Fax: USA +1-202-289-4950 Policy Programs E-mail: [email protected] 1200 New York Ave., NW Web: www.aaas.org/spp/bgenes/ Washington, D.C. 20005 This report is also available on the Web: Layout and cover design by http://www.aaas.org/spp/bgenes/ AAAS Publication Services. publications.shtml Preparation and publication of this volume was supported by a grant from the National Human Genome Research Institute (RO1 HG001873) and by contributions to the AAAS Fund for Excellence designated for the Directorate for Science & Policy Porgrams. II BEHAVIORAL GENETICS TABLE OF CONTENTS Preface. VI–VII Introduction . VII–X Acknowledgements . XI 1. What is behavioral genetics? . 1 Margaret, an ambitious mother . 1 Defining behavior . 2–3 Forms of behavior . 3–4 Behavioral genetics . 4–5 Margaret’s ambition . 5–6 Science in society . 6 2. How do genes work within their environments? . 9 Hoda, a perplexed nurse . 9 The human genome . 10 Function of the human genome . 10–13 Variety within the human genome. 13–14 Similarity across genomes. 14–15 Imagining the genome . 16–17 Behavior and the genome . 17–18 Hoda’s perplexity . 18–20 Some caveats . 20–21 3. How do environments impinge upon genes? . 25 Skip, a regretful man. 25 Environment illustrated. 26–28 Gene/environment interactions . 28–29 Developmental noise . 30 Gene/environment correlations . 31 Shared and nonshared environments . 31–33 Heritability (and environmentability) . 33–34 Skip’s regrets. 34–35 Developmental pathways . 36 TABLE OF CONTENTS III 4. How is genetic research on behavior conducted? . 39 Anja, an identical twin . 39 Animal studies . 40–41 Family studies. 42 Twin studies . 42–44 Adoption studies . 44–45 Combined studies. 45 Linkage analysis. 45–47 Association studies . 48 Microarray analysis . 48–49 Knockout studies . 49–50 Anja’s question. 50–51 Concerns about non-molecular research . 51–53 Concerns about molecular research . 54–55 Overcoming the research concerns . 55–56 5. How do mental disorders emerge from the mix of genes and environments? . 59 Lamar, a man with bad news . 59 Genotype/phenotype complexity . 60–62 More genotype/phenotype complexity . 62–63 Polygenic disorders: complexity multiplied . 63–64 Schizophrenia, a polygenic disorder . 64–65 Bipolar disorder, also polygenic . 66–67 Research challenges. 67–68 Lamar’s dilemma. 68–70 Normal and abnormal traits. 71 IV BEHAVIORAL GENETICS 6. How is the ability to control impulses affected by genes and environments? . 75 Trevor, in trouble with the law . 75 Impulsive behavior and ADHD . 76–78 Is ADHD a disorder or a trait? . 78–79 Novelty-seeking: a positive impulsive trait . ..