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Frida Kahlo (1907–1954). My Grandparents, My Parents, and I (Family Tree), 1936.Museum of Modern Art, New York.
THE PROCESS OF GENETIC TRANSMISSIONChromosomes and GenesGenes, DNA, and ProteinsGENETIC INFLUENCES ON DEVELOPMENTThe Transmission of Traits: A Basic ModelGenes on the Sex Chromosomes: Exceptions to the RuleInteractions Among GenesGenetic DisordersBOX 2-1 Risk and Resilience: Sickle-Cell Anemia: A Double-Edged SwordGENETIC COUNSELING AND GENETIC ENGINEERINGPrenatal Diagnostic TechniquesBOX 2-2 Child Psychology in Action: The New Reproductive TechnologiesGene TherapyHEREDITY-ENVIRONMENT INTERACTIONSBOX 2-3 Child Psychology in Action: The Human Genome ProjectHow the Environment Influences the Expression of GenesHow Genetic Makeup Helps to Shape EnvironmentHEREDITY, ENVIRONMENT, AND INDIVIDUAL DIFFERENCESMethods of Studying Individual DifferencesSome Individual Differences and Their ContributorsMAKING THE CONNECTIONS 2SUMMARYEXPLORE AND DISCUSS2.Heredity and the EnvironmentOne of the most striking things about newborns in a hospital nurs-ery is their diversity. From the moment they’re born, babies differ from one another not only in physical appearance but also in behav-ior. One baby may sleep most of the time; another may be quite alert, visually scanning the surroundings as if exploring them; a third baby may be irritable and cry a lot. What contributes to these individual differences at such a young age? Transactions among a vast array of hereditary and environmental factors begin before birth. Such transactions between genes and the environment make each newborn unique, and they continue to shape the individual’s characteristics throughout his or her life.The concepts of genotype and phenotype provide a framework for exploring the interactions of genes and environment. A genotypeis the particular set of genes that a person inherits from his or her parents and that determines such characteristics as height and eye color. With the exception of identical twins, no two people have exactly the same genotype. During the course of development, the genotype interacts with the environment to produce the phenotype, which is the observable and measurable genetic expression of an individual’s physical and behavioral characteristics. Psychologists study these kinds of characteristics—for example, motor abilities, intellectual skills, social behavior, emotionality, and personality traits—to increase our understanding of how genetic and environ-mental factors interact to produce each unique human being.We begin this chapter by exploring what genes are and how they are transmitted from generation to generation. Next we examine how genes guide development, from determining a child’s sex to countless other characteristics. We go on to examine genetic testing and counseling for would-be parents who face the prospect of hav-ing a child with a troubling disorder, and we explore the growing fi eld of genetic engineering. Then we consider heredity- environment interactions. We discuss both the ways environmental factors influ-