PSYCH 127B Lecture Notes - Lecture 2: Thomas Kuhn, Gene Expression, Heritability
Week 1 – Lecture 2: Genetic Bases of Abnormal Behavior
Psych 127B Lecture Outline – Midterm 1 Review
I. Notion of a Paradigm
a. Goal: Study abnormal behavior scientifically
b. Science aims for objectivity
c. Paradigm (Thomas Kuhn)
i. Perspective or conceptual framework from within which a scientist operates
1. We can never be totally objective
d. No one paradigm sufficient to completely explain psychopathology
II. Genetic Paradigm
a. Heredity plays a role in most behavior
b. Genes
i. Carriers of genetic information (DNA)
ii. Impacted by environmental influences
1. e.g., stress, relationships, culture
c. Relationship between genes and environment is bidirectional
i. Nature via nurture (Ridley, 2003)
III. Behavior Genes
a. Study of the degree to which genes and environmental factors influence behavior
b. Genotype
i. Genetic material inherited by an individual
ii. Unobservable
c. Phenotype
i. Expressed genetic material
ii. Observable behavior and characteristics
iii. Depends on interaction of genotype and environment
IV. Important Genetic Terms
a. Gene expression» Proteins influence whether the action of a specific gene will occur
b. Polygenic transmission» Multiple gene pairs vs. single gene
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Week 1 – Lecture 2: Genetic Bases of Abnormal Behavior
c. Heritability» Extent to which variability in behavior is due to genetic factors
i. Heritability estimate ranges from 0.00 to 1.00
ii. Group, rather than, individual indicator
V. Heritability: Definition
a. Heritability is the extent to which genetic individual differences contribute to individual
differences in observed behavior.
b. Statistical definition: Heritability is the proportion of phenotypic variance attributable to
genetic variance.
VI. Heritability
a. Heritability is a proportion; therefore its numerical value will range from 0.0 (i.e., genes do
not contribute at all to the phenotypic individual differences) to 1.0 (genes are the only
reason for individual differences).
b. For human behavior, estimates of heritability are generally in the moderate range of .30 to
.60.
VII. Environmentability
a. Environmentability is the proportion of the phenotypic variance attributable to
environmental variance.
b. 1.0 – heritability = environmentability
c. Given that heritability of most human behaviors is in the range of .30 to .60 then the
environmentability of most behaviors is in the range of .40 to .70.
VIII. Heritability: Key Concepts
a. Heritability and environmentability are abstract concepts. They tell us nothing about the
specific genes and environmental factors contributing to a trait.
b. Heritability and environmentability are population concepts. They tell us nothing about an
individual.
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