PSYA02H3 Chapter Notes - Chapter 9.3: Long-Term Potentiation, Gene Knockout, Twin
Module 9.3: Biological, Environmental and Behavioural Influences on
Intelligence
Biological Influences on Intelligence
Genetics of Intelligence: Twin and Adoption Studies
- Genetic similarity (twins and adopted children) does contribute to intelligence test scores
- As genetic relatedness increases, similarity in IQ scores increases as well
- The intelligence scores of identical twins correlate with each other at about .85 when they are raised
in the same home, which is much higher than the correlation for fraternal twins. Even when identical
twins are adopted and raised apart, their intelligence scores are still correlated at approximately
.80—a very strong relationship. In fact, this is about the same correlation that researchers find when
individuals take the same intelligence test twice and are compared with themselves!
Heritability of Intelligence : figure 9.13
- Heritability of intelligence estimated to be 40%-80%
- Describes how much of the differences between people in a sample can be accounted for by
differences in their genes
- Means that heritability estimate is not a fixed number but a number that depends on sample of
people being studied
- i.e. heritability for wealthy people=72% & poor=10%
- Estimates depend on other factors such as how different/similar people’s environments are
- we understand that nurture shapes nature; that is, environmental factors determine how genes
express themselves and influence the organism.
- Problems with interpreting heritability estimates as indications that genes cause differences in
intelligence
o Environmental factors determine how genes express themselves and influence the organism
o Genes that influence intelligence may do so, indirectly, operating through other factors
Behavioural Genomics
- Behavioural genomics: a technique that examines how specific genes interact with the environment
to influence behaviours, including those related to intelligence
o Main focus is to identify genes that are related to cognitive abilities such as learning and
problem solving
o However, although almost 300 individual genes have been found to have a large impact on
various forms of mental retardation (Inlow & Restifo, 2004), very few genes have been found
to explain normal variation in intelligence (Butcher et al., 2008). In one large study that
scanned the entire genome of 7000 people, researchers found a mere six genetic markers
that predicted cognitive ability.Taken together, these six markers only explained 1% of the
variability in cognitive ability
- Gene knockout studies: removing a specific gene and comparing the characteristics of animals with
and without that gene
o In one experiment, researchers learned that by removing one gene, mice lost ability to learn
spatial layouts
o since this investigation was completed, numerous studies using gene knockout methods
have shown that specific genes are related to performance on tasks that have been adapted
to study learning and cognitive abilities in animals
- Transgenic: inserting genetic chromosomes rather than removing them and examining behavior
- One now-famous example is the creation of Doogie mice, named after the 99s TV character
Doogie Howser (played by a young Neil Patrick Harris), a genius who became a medical doctor while
still a teen- ager. Doogie mice were created by manipulating a single gene, NR2B (Tang et al.,
1999).This gene encodes the NMDA receptor, which plays a crucial role in learning and memory.
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Document Summary
Module 9. 3: biological, environmental and behavioural influences on. Genetic similarity (twins and adopted children) does contribute to intelligence test scores. As genetic relatedness increases, similarity in iq scores increases as well. The intelligence scores of identical twins correlate with each other at about . 85 when they are raised in the same home, which is much higher than the correlation for fraternal twins. Even when identical twins are adopted and raised apart, their intelligence scores are still correlated at approximately. In fact, this is about the same correlation that researchers find when individuals take the same intelligence test twice and are compared with themselves! Heritability of intelligence estimated to be 40%-80% Describes how much of the differences between people in a sample can be accounted for by differences in their genes. Means that heritability estimate is not a fixed number but a number that depends on sample of people being studied i. e. heritability for wealthy people=72% & poor=10%
