Behavioral genetic
methodologies from twin and adoption studies through DNA analysis will be
described and applied to address longstanding questions about the origins of
individual differences in behavioral traits.
Syllabus
· 1
o Unit # 1: Course
Introduction and OverviewOverview: Unit # 1 provides an overview to the field
of human behavioral genetics and to this course. We will begin by discussing
the early history of the field and how behavioral genetic research influenced
and was influenced by the eugenics movement. Once this historical context has
been established, we will define the field of behavioral genetics and use this
definition to provide an overview of the course. This week’s lectures will end
with two case studies that illustrate the importance of behavioral genetic
approaches. The first is the famous John/Joan case, where one member of a
monozygotic twin pair was raised as a boy and the other as a girl. The second
is the human genetic disorder Phenylketonuria (PKU), which has been recognized
as a paradigm of human genetic disease since its discovery in 1934.Unit
Objectives: At the end of this unit you should know• The history of the
founding of the field of behavioral genetics• What the eugenics movement was
and how it impacted psychology and behavioral genetics• What the field of
behavioral genetics covers• How the John/Joan case represented the extreme of
the “Blank Slate” mentality within psychology• Why Phenylketonuria is
considered a public health success and model of human genetic diseaseLecture
Modules:A. The Nature-Nurture Debate and Founding of Behavioral GeneticsB. The
Eugenics MovementC. What is Behavioral GeneticsD. The John/Joan CaseE.
Phenylketonuria (PKU) F. Huntington Disease (Supplemental)
· 2
o In Unit #2 the twin
study method will be introduced and general findings from twin studies in
psychology and psychiatry will be reviewed. The two types of twins, monozygotic
(MZ) and dizygotic (DZ), will be described and methods for assessing their
similarity will be given. We will also look critically at the limitations of
the twin study method and discuss alternative research designs, including
adoption studies and the study of reared-apart twins. The importance of convergent
evidence from multiple research designs will be emphasized.
· 3
o Some of the most
contentious issues in behavioral genetics surround the concept of heritability
– Is it a meaningful statistic? Can it be accurately estimated in studies on
humans? How should it be interpreted? In this unit we will discuss what is
meant by heritability and describe some simple biometric (i.e., quantitative
genetic) methods used for it estimation. The unit begins with a review of basic
Mendelian inheritance and the introduction of some genetic terminology we will
begin to use in the course. The ACE model of quantitative inheritance is
described and we will discuss how this model is used to analyze twin data.
Finally, the important concept of gene-environment interaction is formally
introduced. Beginning this week with quantitative genetics and continuing next
week with molecular genetics we will be jumping head first into the thicket of
human genetic methodology. For some, this material may be more challenging than
that which we covered in the first two weeks of this course. These weeks will,
however, provide the foundation we will need to investigate in depth behavioral
genetic research on schizophrenia and intelligence in weeks 5 and 6. Please
make sure to post questions you have to the discussion forums and especially to
the office hours forum.
· 4
o The Human Genome
Project (HGP) was begun in 1990 and declared complete in 2003. It has
revolutionized our understanding of genetics and will ultimately revolutionize
medical practice. In my opinion, every educated citizen should know some basic
findings from the HGP. This week’s lectures provide an introduction to
molecular biology and the HGP. We will cover topics such as: What is DNA? What
is a gene and how are genes structured? In what ways can human genomes differ?
What is epigenetics and why do some researchers believe it is very important
for understanding behavior? As in previous lectures, I will illustrate some of
the basic human genetic phenomena through case studies, in this case ranging
from calico cats to the human genetic disorders of Angelman and Prader-Willi
syndromes.
This week’s lectures continue what we began last week: laying the foundation of
genetic concepts and processes we will need to consider in some depth genetic
research on schizophrenia and intelligence. Some participants in this course
already have an extensive background in basic genetics and so will be very
knowledgeable about material covered in the initial modules. But I think even
these participants will have something to learn when we get to the later
modules in the unit covering, e.g., Williams Syndrome, Prader-Willi Syndrome
and Angelman Syndrome. For those with a more limited background in genetics, I
recognize that the terminology introduced this week may at first seem a bit
daunting. But if you stick with it, terms such as SNPs, methylation, exon, copy
number variants, etc. which seem foreign now will become consolidated in your
vocabulary through repeated use throughout the remaining lectures in this
course.
There are several learning aids I would encourage you to use. First, we have
created a Glossay, which you can link to off the navigation bar on the course
website. Second, the Discussion Forums are a wonderful source of help. Other
participants can be very helpful in answering your questions and a post in the
Office Hours thread will be reviewed by us for response in the weekly office
hour video. Finally, we give again online genetics education links in the Other
Resources section below.
· 5
o Now that we have a
foundation in basic biometric and molecular genetics we can begin to look in
depth at genetic research for behavioral phenotypes. This week we will focus on
schizophrenia. There are several reasons for this focus. First, genetics
research has fundamentally changed the way researchers and mental health
professionals think about this devastating illness; schizophrenia illustrates
the successes as well as the limitations of the genetic approach to a
psychiatric illness. Second, research on schizophrenia exemplifies what genetic
researchers are finding with most common mental illnesses. Although, for
example, the exact chromosomal locations of risk variants and the specific
candidate genes implicated certainly vary from one psychiatric illness to the
next, the basic features of the genetic architecture appears to be remarkably
similar across multiple psychiatric illnesses, at least at this time. So an
understanding of the genetics of schizophrenia will bring with it an
understanding of much of psychiatric genetics.
Before discussing the genetics research, however, I think it useful that we all
know at least a little about what schizophrenia is. Thus the first two modules
in this unit describe the clinical phenotype and some of its basic
epidemiology, information that will no doubt be very familiar to those of you
with a background in clinical psychology or psychiatry. Twin and adoption
studies helped to establish the heritable nature of schizophrenia (Module C)
and characterize the nature of environmental influence (Module D). The current
frontier in genetics research on schizophrenia is to identify the specific
genetic variants that underlie its heritability. Initial attempts at
identifying risk alleles using the positional cloning strategy were generally
unsuccessful yet provided key insights into the nature of the disorder (Module
E). Very recently, important breakthroughs have been achieved through Genome
Wide Association Studies (GWAS; Module F) and rare variant analysis (Module
G). Although the basic foundation for this course was introduced in Units
1-4 and we strive to minimize our use of jargon, sometimes the technical term
is exactly what is needed and we will continue to introduce new terms
throughout the remainder of the course. So please make use of the Glossary
(linked on the navigation bar). We created it in the hope it would help
minimize the impact technical jargon might have on your mastering the lecture
material.
· 6
o If there is an area of
psychology that generates more heated debate than behavioral genetics it would
be the field of intelligence research. While most of us acknowledge the
differences among us in personality and even risk for mental illness, for some
of us differences in intelligence seem more difficult to accept. I confess I am
not completely sure why this is the case. Maybe it is because of the
involvement of early intelligence researchers with the Eugenics Movement.
Alternatively, maybe it is because the conclusions reached by some intelligence
researchers seem to challenge our long-held beliefs about social equality,
especially when those conclusions are biologically grounded. Regardless,
intelligence, or as I prefer to call it general cognitive ability (GCA), has
been a major focus of behavioral genetic research and we will use it as a
prototype of behavioral genetic research on a quantitative psychological
trait.As with the previous unit, we will begin with a brief discussion of what
psychologists mean by intelligence or GCA. I will not try and review the vast
empirical literature on the correlates of GCA; suffice to say that GCA is
correlated, not always strongly, with many desirable outcomes including
educational attainment, occupational achievement, health, mortality, criminal
conviction, etc. Twin and adoption studies of GCA have implicated the
importance of both genetic and nonshared as well as shared environmental
influences. Behavioral genetic research has helped to identify features of the
shared environment that appear to contribute to differences in intelligence,
but, unlike with schizophrenia and other mental illnesses, it has been
difficult to identify the specific genetic variants that contribute to the
heritability of GCA. This unit will end with a discussion of genetic research
on intellectual disability, an important application of intelligence
research.Just FYI, one thing we will NOT consider in this unit but some of you
will wonder about is developmental behavioral genetic research on intelligence.
I promise that it will be covered in Unit 7.
· 7
o I am sure many of you
wondered about the impact of age on biometric estimates when we discussed
general cognitive ability last week. Indeed some of you asked about this issue
on the Forums. You were right to raise the question because this is an
important issue in the behavioral genetic literature. Given its importance, I
thought it might work best to place the question of age moderation in a larger
context, which we do this week. We will begin the week by returning to the
distinction between shared and non-shared environmental influences, an
important distinction in the behavioral genetic literature. You will see that
while shared environmental influences are not important for most behavioral
phenotypes, there are a few exceptions (including general cognitive ability).
However, in all of these exceptional cases, the magnitude of shared
environmental influences decreases with age as the heritability increases.
To understand this developmental pattern, at least from a behavioral genetic
perspective, it is helpful to consider mechanisms of gene-environment
correlation as well as behavioral genetic perspectives on family socialization.
We end this unit with an overview of behavioral genetic research on aging.
· 8
o It is hard to believe
we are already to the 8th and final week of the course. This unit begins with
an overall summary of human behavioral genetic research organized around four
general findings, or ‘laws’ of behavioral genetic research. We will then
consider, I suppose more accurate speculate about, the application of
behavioral genetic research in the field of individualized or genomic medicine
and the implications of behavioral genetic research for personal
responsibility. This week’s lectures will also include an interview with
Professor Irving Gottesman, a pioneer in the field who undertook pioneering
behavioral genetic research on schizophrenia and personality.
Taught
by Mohammed Oirdi
