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they try they are not likely to be able to turn their children into geniuses or into professional
athletes, nor will they be able to turn them into criminals.
If parents are not providing the environmental influences on the child, then what is? The last
column in Table 11.6 "Data From Twin and Adoption Studies on the Heritability of Various
Characteristics", the influence of nonshared environment, represents whatever is “left over” after
removing the effects of genetics and parents. You can see that these factors—the largely
unknown things that happen to us that make us different from other people—often have the
largest influence on personality.
Studying Personality Using Molecular Genetics
In addition to the use of behavioral genetics, our understanding of the role of biology in
personality recently has been dramatically increased through the use of molecular genetics,
which is the study of which genes are associated with which personality traits (Goldsmith et al.,
2003 Strachan & Read, 1999). [7]These advances have occured as a result of new knowledge
about the structure of human DNA made possible through the Human Genome Project and
related work that has identified the genes in the human body (Human Genome Project,
2010). [8] Molecular genetics researchers have also developed new techniques that allow them to
find the locations of genes within chromosomes and to identify the effects those genes have
when activated or deactivated.
One approach that can be used in animals, usually in laboratory mice, is the knockout study. In
this approach the researchers use specialized techniques to remove or modify the influence of a
gene in a line of “knockout” mice (Crusio, Goldowitz, Holmes, & Wolfer, 2009). [9] The
researchers harvest embryonic stem cells from mouse embryos and then modify the DNA of the
cells. The DNA is created such that the action of certain genes will be eliminated or “knocked
out.” The cells are then injected into the embryos of other mice that are implanted into the
uteruses of living female mice. When these animals are born, they are studied to see whether
their behavior differs from a control group of normal animals. Research has found that removing
or changing genes in mice can affect their anxiety, aggression, learning, and socialization
patterns.