RESEARCH METHODS
“In family studies, researchers assess hereditary influence by examining blood relatives to see how much they resemble one another on a specific trait. If heredity affects the trait under scrutiny, researchers should find trait similarity among relatives. Furthermore, they should find more similarity among relatives who share more genes. For instance, siblings should exhibit more similarity than cousins.”
“In twin studies, researchers assess hereditary influence by comparing the resemblance of identical twins and fraternal twins with respect to a trait. The logic of twin studies hinges on the genetic relatedness of identical and fraternal twins (see Figure 3.21). Identical (monozygotic) twins emerge when a single fertilized egg splits for unknown reasons. Thus, they have exactly the same genetic blueprint; their genetic overlap is 100%. Fraternal (dizygotic) twins result when two separate eggs are fertilized simultaneously. Fraternal twins are no more alike in genetic makeup than any two siblings born to a pair of parents at different times. Their genetic overlap averages 50%.”
Adoption studies assess hereditary influence by examining the resemblance between adopted children and both their biological and their adoptive parents. If adopted children resemble their biological parents on a trait, even though they were not raised by them, genetic factors probably influence that trait. In contrast, if adopted children resemble their adoptive parents, even though they inherited no genes from them, environmental factors probably influence the trait.
“contrary to early expectations for genetic mapping techniques, it appears that scientists are not likely to identify a handful of specific genes that control intelligence, extraversion, musical talent, or other behavioral traits, including psychological disorders. That reality does not mean that genetic mapping studies have no role to play in unraveling the hereditary bases of behavior. Scientists remain optimistic. The challenge will be to identify collections of genes that each exert very modest influence over aspects of behavior and to figure out how these genes interact with environmental factors (Halldorsdottir & Binder, 2017; Heine, 2017).”
. Epigenetics is the study of heritable changes in gene expression that do not involve modifications to the DNA sequence. The effects of certain genes can be inhibited or stopped by chemical changes at the cellular level, and these changes can be heritable even though the genes don’t change. Believed to be partially responsible for psychological disorders and addictive tendencies.