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Lecture 3

PSY100H1 Lecture Notes - Lecture 3: Twin Study, Behavioural Genetics, Quantitative Genetics

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Waggoner Denton Ashley

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Chapter 6: The Nature-Nurture Question:
- Some aspects of our behavior feel as though they originate in our genetic makeup while others feel it is the
result of our upbringing
- Behavior genetics; studying differences in DNA of people with different behavioral traits
- Genes and environments always combine to produce behavior
- 3 related problems at the intersection of philosophy and science: mind-body, free will and nature-nurture
o everyone has opinions about the answers to these questions that come from simple observations of
the world we live in
- We are born with certain characteristics, while others are acquired
o We are so concerned with it because our moral character seems to depend on it
o Its not our fault if we don’t hit the genetic lottery
- When we think about our own qualities, they seem under our control in some respects, yet beyond our
control in others
- Main problem in answering this question is how do we set up an experiment
o Nonhuman animals testing for determinant of aggression among dogs: born to be aggressive or
are they raised?
o We can’t assign babies to parents at random with people
- In typical human families, children’s biological parents raise them so it is difficult to know whether
children act like their parents due to genetics or environmental reasons
- Behavioral genetics: science of how genes and environments work together to influence behavior
- Adoption study: when children are put up for adoption, parents who gave birth to them are no longer the
parents who raise them
- Twin studies: behavior genetic research method that involves comparison of similarity of identical
(monozygotic; MZ) and fraternal (dizygotic; DZ) twins
o 1) Monozygotic = identical twins, single zygote (fertilized egg) and have same DNA; clones
o 2) Dizygotic = fraternal, develop from 2 zygotes and share 50% of DNA, born at the same time
- Quantitative genetics: scientific discipline in which similarities among individuals are analyzed based on
how biologically related they are
o Among siblings and half siblings, cousins, twins separated at birth
o Produces a number called heritability coefficient: varying from 0 to 1 meant to provide a single
measure of genetics’ influence of a trait
Measures how strongly differences among individuals are related to differences among
their genes
- We live in an era of great scientific discovery in genetics new discovered are made everyday
o DNA discovered by Watson and Crick in 1950s
What Have We Learned About Nature-Nurture?
- Everything has turned out to have some footing in genetics
- The more genetically-related people are, the more similar they are
o Same for some psychological traits and political attitudes
- Genetic influence on behavior is recent discovery
- Neither behaviorism nor psychoanalysis is incompatible with genetic influences on behavior
o Can’t leave genes out of the question, but keep in mind, no behavioral traits are completely
inherited, so you can’t leave environment our either
- When your subjects are biologically-related, no matter how clearly a situation may seem to point to
environmental influence, it is never safe to interpret a behavior as wholly with further evidence
o Correlation does not imply causation
- Inability to organize traits from more-to-less genetic; everything has turned out to be somewhat heritable,
but nothing is absolute heritable and there isn’t consistent to which traits are more and less heritable
- Problem = conceptual
- We want to know how ‘important’ the roles of genes and environment are to development of a trait
- Genes and environment are both crucial to every trait
o Without genes the environment would have nothing to work on
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