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.
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)
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.
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.
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.
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.
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.