3: Genes and Behavior

Introduction

• Genes, Genetic Analysis, and Heritability in Behavior

• The Nature of the Gene

• Genes Are Arranged on Chromosomes

• The Relationship Between Genotype and Phenotype

• Genes Are Conserved Through Evolution

• The Role of Genes in Behavior Can Be Studied in Animal Models

  • Circadian Rhythm Is Generated by a Transcriptional Oscillator in Flies, Mice, and Humans

  • Natural Variation in a Protein Kinase Regulates Activity in Flies and Honeybees

  • The Social Behaviors of Several Species Are Regulated by Neuropeptide Receptors

• Genetic Studies of Human Behavior and Its Abnormalities

  • Neurological Disorders in Humans Suggest That Distinct Genes Affect Different Brain Functions

  • Autism-Related Disorders Exemplify the Complex Genetic Basis of Behavioral Traits

• Psychiatric Disorders and the Challenge of Understanding Multigenic Traits

  • Complex Inheritance and Genetic Imprinting in Human Genetics

  • Multigenic Traits: Many Rare Diseases or a Few Common Variants?

• An Overall View

• Glossary

All behaviors are shaped by the interplay of genes and the environment. The most stereotypic behaviors of simple animals are influenced by the environment, and the highly evolved behaviors of humans are constrained by innate properties specified by genes. Genes do not control behavior directly, but the RNAs and proteins encoded by genes act at different times and at many levels to affect the brain. Genes specify the developmental programs that assemble the brain and are essential to the properties of neurons and synapses that allow neuronal circuits to function. Genes that are stably inherited over generations create the machinery that allows new experiences to change the brain during learning.

In this chapter we ask how genes contribute to behavior. We begin with an overview of the evidence that genes do influence behavior, and then review basic principles of molecular biology and genetic transmission. We then provide a few examples of the way that genetic influences on behavior have been documented. Many persuasive links between genes and human behavior have emerged from the analysis of human brain development and function. However, a deep understanding of the ways that genes regulate behavior has emerged primarily from studies of worms, flies, and mice, animals whose genomes are accessible to experimental manipulation. Despite formidable challenges in studying complex genetic traits in humans, recent progress has revealed the genetic basis of some developmental and psychiatric disorders, and holds the promise of future understanding.

Genes, Genetic Analysis, and Heritability in Behavior

Many human psychiatric disorders and neurological diseases have a genetic component. The relatives of a patient are more likely than the general population to have the disease. The extent to which genetic factors account for traits in a population is called heritability. The strongest case for heritability is based on twin studies, first used by Francis Galton in 1883. Identical twins develop from a single fertilized egg that splits into two soon after fertilization; such monozygotic twins share all genes. In contrast, fraternal twins develop from two different fertilized eggs; these dizygotic twins, like ...