Genes for Genius?
Overview | Article Summary
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Students
Chorney, M.J., Chorney, K., Seese, N., Owen, M.J., Daniels, J., McGuffin,
P., Thompson, L.A., Detterman, D.K., Benbow, C., Lubinski, D., Eley, T.
and Plomin, R. (1998). A quantitative trait locus associated with cognitive
ability in children. Psychological Science, 9, 159-166.
Overview:
Behavior Genetics
The nature-nurture controversy has raged since long before the terms were
coined in the 16th century. Nature refers to an individual's genetic
make-up and nurture refers to environmental influences over behavior.
Most psychologists acknowledge that genetics and the environment combine
in different ways to influence behavior. Behavior geneticists investigate
the relative influence of genetics and the environment on behavior.
Family studies are commonly used to examine the influence of
genetics and the environment on behavior. In a family studies, behaviors
are tested over several generations to trace the inheritance of some behavior.
Related to family studies are twin and adoption studies.
Identical or monozygotic twins share the same genetic material and a similar
environment. Fraternal or dizygotic twins share as much genetic material
as siblings but do have a similar environment. If monozygotic twins are
more a like than dizygotic twins on some measure then behavioral geneticists
relate this difference to genetics. In adoption studies, children are compared
with their biological and their adoptive parents. If the child's behavior
more closely resembles the biological parent then genetic factors are implicated.
These studies can only point out behaviors that may be influenced by
genes. Genetic mapping is being used to determine the location and function
of specific genes on specific chromosomes. These genetic maps have been
used to identify genes responsible for various disorders, such as Huntington's
disease, a progressive disorder characterized by muscle deterioration,
personality change and intellectual decline in adults who carry the gene.
The Human Genome Project is a massive collaborative effort to map out human
genes and address ethical, social, and scientific issues related to human
genetics.
Mapping out human genes is an enormous undertaking. Deteriming what
sorts of influences these genes have is even more enormous, particularly
since much of human behavior appears to be polygenetic, that is, influenced
by more than one gene. Intelligence is one form of human behavior that
is polygenetic. Psychologists are still defining and refining the concept
of intelligence and how to measure intelligence. Chorney, Chorney, Seese,
Owen, Daniels, McGuffin, Thompson, Detterman, Benbow, Lubinski, Eley, and
Plomin (1998) have begun to look for genetic contributions to intelligence
using state-of-the-art genetic mapping techniques. Their collaborative
efforts have yielded a gene that makes a very small but potentially important
contribution to intelligence.
Overview | Article Summary | For
Instructors | For Students
Article Summary
Family, twin, and adoption studies indicate that genes have some influence
on intelligence. Identifying the genetic influence is a monumental task,
however. Genetic mapping is easiest when a gene operates in an all-or-none
fashion, such that when the gene is present, so is some behavior or trait
and when the gene is absent, so it the associated behavior or trait. But
intelligence is not all-or-none, intelligence has a roughly normal distribution
in the population. Intelligence is also strongly influenced by the environment
and the interaction between genes and the environment, making it difficult
to isolate the independent effect of genes on intelligence. Finally, intelligence
is most likely polygenetic, influenced by multiple genes, combining in
multiple ways to influence intelligence.
Chorney, Chorney, Seese, Owen, Daniels, McGuffin, Thompson, Detterman,
Benbow, Lubinski, Eley, and Plomin (1998) recognized these three aspects
of the relationship between genes and intelligence. They began their research
on the assumption that the genetic influence on intelligence likely involves
quantitative trait loci (QTLs) -- genes that have a small and differing
effect on behavior.
Because individual genes are likely to have a small effect on intelligence,
Chorney et al. selected people with extremely high scores on intelligence
tests and compared them with people who have average IQs. They looked for
genetic differences on the long arm of Chromosome 6 because that is one
of the Chromosomes being mapped completely through the Human Genome Project.
Genetic differences between groups of people with high and average IQ were
used to identify genes that might influence intelligence.
Chorney et al. (1998) examined differences between 37 different genes
on the long arm of Chromosome 6. One gene, IGF2R, showed a difference between
the two groups. This gene has at least seven different molecular forms,
or alleles. Two of these alleles were most frequently obtained, and one
allele, Allele 5, was more common in the extremely high IQ group (46% had
at least one IGF2R Allele 5) than in the average IQ group (23% had at least
one Allele 5). Presence of this allele accounted for 2% of the variance
in IQ or about 4 IQ points.
IGF2R is a gene that codes for a receptor for an insulin-like hormone
but its function in the organism is not known. This gene is also at one
part of the chromosome that may not even be functional. Since only a portion
(37 genes) of this chromosome has been mapped, it may be entirely likely
the IGF2R is not even the QTL for the effect but close to another gene
that does have an effect.
Allele 5 of the IGF2R gene accounts for 4 IQ points? IGF2R may not even
be functional? With such a small effect of a gene that may not even be
the real gene, why was this study reported? This study is important for
two reasons. This research clearly demonstrates that the influence of genetics
on complex human cognition is multifactorial. The team that conducted this
research, made up of preeminent molecular biologists and behavior geneticists,
are not looking for the "gene for genius" but for subtle genetic differences
that might have some influence on the complex set of cognitive abilities
that we call intelligence. This research is also the first attempt to directly
isolate genes that differ between groups rather than make inferences based
on family resemblance (or lack or resemblance).
Overview | Article Summary
| For Instructors | For Students
For Instructors
Links to the Lecture
IQ Tests
Chorney et al. report on a gene that accounts for 2% of the variance
in general intelligence. How valid and reliable is IQ? Check out the December
Instructors Resources for a classroom activity on IQ testing.
Ethics
Chorney et al. argue that because IGF2R accounts for at most 2% of the
variance in intelligence between high intelligence and average intelligence
groups, such a marker would never be useful for genetic testing or discrimination.
This argument provides a good topic for discussion. Do students agree with
Chorney et al.'s argument? How many genes need to be identified before
there is a potential for genetic testing for intelligence? Are there any
concerns about searching for "genes for genius"?
Overview | Article Summary
| For Instructors | For Students
For Students
About the Authors
This research is the result of collaboration among researchers at a number
of different universities. Researchers from each university contributed
in their area of expertise. For example, Detterman and his group are experts
in behavioral genetics, and Plomin and his group are experts in intelligence
testing.
Michael and Karen Chorney and Nicole Seese are in the Department of
Microbiology in the School of Medicine, Pennsylvania State University.
Mike Owen, J. Daniels, and Peter
McGuffin are in the Department of Psychological Medicine at the University
of Wales School of Medicine.
Lee Thompson
and Douglas Detterman are in the Department of Psychology at Case Western
Reserve University.
Camilla
Benbow and David
Lubinski are in the Department of Psychology at Iowa State University.
T.Eley and Robert Plomin are in the Institute of Psychiatry, Kings College
London.
About the Journal
Psychological
Science Is a journal of the American
Psychological Society.
Links to Life
Ethics and Genetics
Here is an interesting paper,
reprinted from the American Journal of Human Genetics on ethical and scientific
issues regarding human behavioral genetics. This paper also includes a
brief review of different research methods, including QTL.
Here is a list
of links to sites concerned with ethical issues related to the Human
Genome Project. The National Bioethics Advisory Commission Report deals
with cloning humans. The University of British Columbia site includes links
to public action groups ? these groups have varying statements on the ethics
of genetics research.
Learn About Genetics
To learn more about genetics, check out this Primer
on Molecular Genetics from the Department of Energy which sponsors
the Human Genome Project. Check out the Introduction to learn more about
DNA, genes, and chromosomes, then read about genetic mapping strategies
in the next section.
CNN
has a glossary of genetics terms, news reports on genetic research, and
links to other sites.
Here is the website
for the Human Genome Project, dedicated to mapping human genes.
This site contains
a java applet for performing QTL. Advanced genetics students may be interested
in working through the examples. Otherwise, this site is included to show
the power of the Web for collaborating on research.
What Is Intelligence?
Check out some of the following intelligence tests. What are these tests
measuring? How would you define intelligence?
-
IQ Test by Cyberia Shrink
-
IQ Test
by William F. Bultas. Ten very difficult items.
-
IQ Test from
Braintainment. A tricky 5 min. timed sentence completion task. Your test
score results will come with an advertisement for buying their product.
-
Mensa Workout. Sample items
from a test used to qualify for Mensa, an organization for high IQ people.
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