III. Types of Genetic Studies
Researchers do different kinds of studies to see whether and to what extent a characteristic might be genetically transmitted. Family Studies In family studies, researchers look at similarities among members of a family with respect to a particular trait. If the trait is genetically inherited, it should be similar in blood relatives. The closer the blood relationship, the more similar people should be. Family studies alone don’t reveal whether a trait is genetically inherited. A family shares genes, but they also share similar environments. When researchers find trait similarity in a family study, their findings may suggest that the trait is genetically inherited, but the study can’t prove it. Twin Studies Compared to family studies, twin studies give researchers more solid evidence about whether a trait is inherited. In twin studies, researchers compare pairs of identical twins to fraternal, or nonidentical, twins. When doing these studies, researchers assume that identical twin pairs share the same environment, just as fraternal twin pairs do. However, identical twins share all of their genes with each other, while fraternal twins share only half of their genes. When a trait shows more similarity between identical twins than between fraternal twins, the greater similarity probably comes from shared genes, not shared environment. One problem with this type of study is that identical twins may not in fact share an identical environment while fraternal twins do. People tend to treat identical twins in unusual ways. For example, people may treat identical twins as if they are similar in every respect, or they might focus intensely on differences between them. Studies of Separated Twins In order to avoid uncertain environmental factors, researchers sometimes study separated twins. Twins who are separated when they are very young and brought up in different families have different environmental influences but identical genes. Trait similarities between separated twins result mostly from genes. However, separated twin studies can also be problematic. The environments of separated twins may not actually be that different from each other for the following reasons:
Experiences and Behavior Experiences affect behavior partly because environmental stimulation forms and maintains neural connections. For example, psychological research shows that babies need consistent, loving contact with a caregiver in order to achieve optimal brain development. Neglected babies, lacking attention and physical contact, experience unpleasant emotions that are not simply transitory. Their experiences determine the development of their neural connections. Similarly, soldiers on active combat duty can suffer mental damage from the continuously stressful environment, even if they never experience physical injury. Adoption Studies In adoption studies, researchers compare adopted children to their biological parents and to their adoptive parents. Adopted children share more genes with their biological parents. The children’s living environments, however, more closely resemble the environments of their adoptive parents. When adoptive children resemble their biological parents more than their adoptive parents with respect to a certain trait, researchers can hypothesize that the trait has a genetic basis. Interaction of Genes and Environment In conducting all these types of studies, researchers have found that while genes influence psychological traits, they don’t act alone. Highly influential environmental factors also play a major role. These factors include:
Cultural Norms Cultural norms are sets of societal expectations that influence behavior. Norms tell us what kinds of behavior are appropriate. For example, in the United States, one cultural norm mandates that children be potty-trained by their third birthday. Parents of children who aren’t potty-trained by that point may start to feel worry, shame, and social pressure as their child’s third birthday passes. Genes and environment interact in complex ways. People usually inherit a vulnerability or predisposition to having a particular psychological trait, and the environment in which those people live shapes the development of that trait. The opposite is also true: people’s psychological traits influence their environments. People don’t just live in environments—they also shape their worlds by exerting their traits. Example: Suppose there are two nonidentical twins, Ben and Tom. Ben is calm by nature, while Tom has always been fussy. Mom and Dad will be more taxed by Tom, so they may be less responsive and patient with him than they are with Ben. Therefore, Tom and Ben experience different parental influences, which may make Tom less trusting than Ben as they grow up. Genes and environment influence Tom’s personality, but the interaction between genes and environment also plays a role. |
Vocabulary to Learn Today
Family Studies Twin Studies Identical Twins Fraternal Twins Adoption Studies |
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