Читать книгу Introduction to Abnormal Child and Adolescent Psychology - Robert Weis - Страница 86

Another way to study the effects of genes on behavior is to examine children’s genes at the molecular (rather than the behavioral) level. Recent advances in our knowledge of the human genome and in gene research technology have allowed scientists to search for specific genes that might be partially responsible for certain disorders (Kornilov & Grigorenko, 2016).

Recall that in neurotypical individuals, genes show natural variation, called alleles. Molecular genetics is the scientific field in which researchers attempt to link the presence of specific alleles with certain attributes, behaviors, or disorders. One way to identify which alleles might be responsible for specific disorders is to conduct a linkage study. In a linkage study, researchers search the entire genetic structure of individuals (i.e., perform a “genome scan”), looking for the presence of certain alleles and the existence of a specific disorder. If researchers find certain alleles in individuals with the disorder and do not find these alleles in people without the disorder, they hypothesize that the allele is partially responsible for the disorder (Schulze & McMahon, 2019).

Researchers tend to use linkage studies when they do not know exactly where to look for genes responsible for the disorder. Given the magnitude of the human genome, it is difficult to identify links between certain alleles and specific disorders. However, researchers have successfully used linkage studies to identify alleles responsible for disorders caused by single genes, such as Huntington’s disease. Linkage studies have been less successful in identifying the causes of disorders that depend on the presence or absence of multiple genes.

An alternative technique is to conduct an association study. In an association study, researchers select a specific gene that they believe might play a role in the emergence of a disorder. Then, they examine whether there is an association between a particular allele of this “candidate” gene and the disorder (Jaffee, 2016).

For example, researchers hypothesized that a specific gene, which affects the neurotransmitter dopamine, might play a role in the development of attention-deficit/hyperactivity disorder (ADHD). They suspected this particular gene because abnormalities in dopamine have been identified as a specific cause for ADHD. Furthermore, medications that affect dopamine in the brain can reduce ADHD symptoms. The researchers identified a group of children with and without ADHD. Then, they examined whether the two groups of children had different alleles for the candidate gene. The researchers found that a certain allele for this gene was much more common among youths with ADHD compared to youth without the disorder. Consequently, they concluded that the gene may be partially responsible for ADHD (Langley, 2019).

Of course, molecular genetics research is much more complicated than has been described here. Nearly all mental disorders are influenced by multiple genes; there is almost never a one-to-one relationship between the presence of a specific allele and the emergence of a given disorder. Furthermore, genes never affect behavior directly; their influence on behavior is always influenced by environmental experience (Kornilov & Grigorenko, 2016).

Review

 Genes come in different variants, called alleles. The alleles we inherit from our parents can influence our physical attributes (e.g., hair and eye color) as well as our risk for developing certain disorders.

 Behavioral geneticists conduct family, adoption, and twin studies to determine the heritability of psychological characteristics like intelligence, personality, and mental health problems.

 Molecular geneticists conduct linkage and association studies to identify specific genes that may underlie certain disorders.