evocative, and active.
Although our biological parents determine our genotype, they also determine the quality of our early environmental experiences. Our genes and early experiences are related. For example, parents with high intelligence may pass on this genetic predisposition to their children. At the same time, because of their high intelligence and (perhaps) income, these parents have access to higher-quality medical care, nutrition, childcare, and schools. Intelligent parents speak and read to their children frequently, provide stimulating educational toys, and take their children on outings. In this manner, their children passively receive genotypes and early environmental experiences conducive to high intelligence.
As children develop, their phenotype gradually emerges from the interaction between their genotype and early environment. Like their parents, they may begin to show signs of above-average intelligence. They show well-developed verbal skills, learn more quickly than their peers, perform more tasks independently, and are curious about a wide range of topics. These behaviors evoke certain responses in others. School personnel may identify these children as gifted and provide them with more enriched educational experiences. They may be admitted into accelerated classes in high school and gain academic scholarships to selective colleges.
As children continue to develop, they actively select environmental experiences conducive to their genotype. For example, they might develop friendships with other bright children with similar interests and hobbies; seek out extracurricular activities that satisfy their curiosity in science, music, or art; and select challenging and rewarding majors in college. In a sense, youths select their own environments based on the cumulative influence of their genes and early experiences.
Now that you know the basics of gene–environment correlation, consider Kirby (From Science to Practice). Can you explain the emergence of Kirby’s problems using the concept of passive, evocative, and active gene–environment correlation?
From Science to Practice: Understanding Gene–Environment Correlation
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Kirby is a 10-year-old boy who attends the third grade at a local public school. Kirby failed first grade and will likely fail again this year. Kirby’s reading is well below average, and he makes frequent mistakes in math. His writing skills are also poor. The school psychologist did not find evidence of a learning disability; however, psychological testing revealed below-average intelligence.
Kirby is frequently disruptive and inattentive during class. His teacher stated that Kirby’s parents “just don’t care.” She has tried to contact his mother by telephone, but she usually does not return her calls and rarely follows through with her suggestions for home tutoring. Kirby will likely be sent to a remedial “special ed” class next year if improvements are not made.
Socially, Kirby is awkward. He is larger and taller than his classmates. He is teased because of his size, his poor grades, and the frequent reprimands he receives from teachers. Classmates also make fun of Kirby because of his name, his old “Walmart clothes,” his poorly cut hair, and the fact that he always “smells like hot dogs”—due to his family’s wood burning stove.
Kirby has few friends in his class. After school, he often hangs around with older kids at the junior high school. Kirby has been caught smoking on a few occasions and teachers also suspect some alcohol use. He is also beginning to pick on younger children after school.
Kirby’s problems include poor academic skills, disruptive behavior at school, and rejection by peers. They can be explained using the three types of gene–environment correlation.
1 Kirby’s parents pass their genes on to him—genes that may have placed him at risk for low academic achievement. Furthermore, his parents also provide him with an early environment that is not conducive to good grades. They may not be able to afford high-quality schools and do not seem involved in his education. Consequently, Kirby struggles with reading and acts out in class.
2 Kirby’s poor academic skills and appearance evoke negative reactions in others. His teacher is frustrated with his antics, and his classmates dislike him.
3 Kirby is beginning to actively select surroundings that are conducive to his genes and emerging disruptive behaviors. Rejected by children his age, Kirby associates with older boys who introduce him to cigarettes and alcohol.
If you were Kirby’s therapist, how might you use the concept of gene–environment correlation to intervene and help Kirby establish a new developmental pathway?
Epigenetics
According to the diathesis–stress model, children will develop a disorder only if they have both a genetic risk for the disorder and an environmental stressor to trigger its onset. Moreover, gene–environment correlations show that our genotype and our environment are not independent; we sometimes select environments that are conducive to our genes. A new area of research called behavioral epigenetics shows that environmental factors can also directly affect the expression of our genes and our risk for mental health problems (Hill & Toth, 2016).
Recall that our genetic makeup consists of DNA, which is organized into genes and chromosomes in each of our cells. Genes direct the building of proteins that allow each cell to specialize and carry out its essential functions. These proteins influence our health, appearance, thoughts, feelings, and actions.
Epigenetic structures consist of chemical compounds and proteins that attach to our DNA and turn genes on or off. These compounds and proteins are not part of our genetic code; consequently, scientists call them epigenetic (i.e., above the genome). When these epigenetic structures attach to DNA and regulate its expression, scientists say they have “marked” the genome. Although these marks do not change the DNA itself, they do alter the way in which cells use the DNA’s instructions. These epigenetic marks can be passed on to new cells when they divide. Moreover, epigenetic marks can also be passed down from one generation to the next.
Epigenetic compounds can affect the expression of DNA in two ways (Image 2.4). In a process called DNA methylation, proteins attach chemical tags (called methyl groups) to certain portions of genes, turning them on or off. In another process called histone modification, DNA wraps either tightly or loosely around histones. Segments of DNA that are loosely wrapped can be expressed, whereas other segments that are tightly wrapped cannot (National Human Genome Research Institute, 2019).
Environmental experiences can change epigenetic structures. Certain environmental factors such as diet, smoking, and exposure to disease have been shown to alter structures, leading to different expressions of the genetic code. Epigenetic structures are heritable. Although much of the epigenome is reset when parents pass their genes to their children, some structures persist and affect the child’s phenotype (Cicchetti, 2019).
www.genome.gov
Researchers at McGill University first demonstrated the effects of epigenetics on behavior in rats (Weaver et al., 2004). Rat pups have a certain gene that regulates their stress response. This gene is wrapped tightly around a histone that prevents it from becoming active. The researchers found
