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Chapter

Psychology 2550A/B Chapter Notes -Twin, Twin Study, Heredity


Department
Psychology
Course Code
PSYCH 2550A/B
Professor
Kelly Olson

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Behaviour genetics studies the role of genes in social behaviour and personality
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GENETIC BASES OF PERSONALITY
The human genome: the genetic heritage
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Each DNA contains about 1.5 gigabytes of genetic information
DNA - long string of small units called nucleotides, 4 types of nucleotides: A, T, G, C
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The analogy that DNA is a blueprint is far from accurate
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They contain a stretch(es) of DNA that specify the structure of a protein to be made
And a stretch called the regulatory sequences, which control whether or not, and how much of, the protein is made
Sometimes different proteins can be made based on the same gene
A gene is a region of DNA that influences a particular characteristic in an organism, and is a unit of heredity
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A small minority of genes are different for different persons and these make each individual genetically distinctive - they are the ones that influence
the diverse variations among people in such characteristics as eye colour and height
Although any unrelated people share about 99.9% of their DNA sequence, people's DNA are not identical (unless identical twins )
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It would not be surprising if the relatively minute variations in the DNA sequences among people can lead to some significant differences in their physical
and behavioural characteristics
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What a cell becomes is determined by biological switches outside the cell that turn the specific genes in the cell on or off
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The goal is to understand just how the genes are turned on and off by the physical and social -psychological environment and expressed, and the specific
ways in which this process influences how we think, feel, and behave
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Studies that compare the similarity in personality shown by individuals who vary in the degree to which they share the same g enes and/or the same
environments
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Genes play a huge role in personality
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TWIN STUDIES
The twin method
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Heredity studies use the twin method to assess genetic influence
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This method compares the degree of similarity on measures of personality obtained for genetically identical twins (those who are from the same
egg/monozygotic, MZ) as opposed to twins who are fraternal (those from a diff fertilized egg, or dizygotic, DZ)
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Identical twins must be more similar than fraternal twins
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Results of twin studies
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The resemblance within identical twin pairs tends to be strongest for general ability - it is somewhat lower for personality inventory scales and lowest for
interests, goals, and self-concepts
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For personality, twin correlations are about .50 for identical twins and .25 for fraternal twins
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The big five
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Extraversion - sociability, impulsiveness, and liveliness
Neuroticism - moodiness, anxiousness, and irritability
Extraversion and neuroticism have been studied the most
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Temperaments
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Temperaments refers to traits that are visible in early childhood and seem relevant to the individual's emotional life
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In adults, they are typically assessed by self-report measures
Assessed through parental reports about their children on temperament
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Some researchers disagree though and find that the intensity with which an individual experiences emotions is independent of how often he or she has
such feelings
Emotionality (aka emotional reactivity) is often defined as the tendency to become aroused easily physiologically (by ready activation of the ANS) and
especially to experience frequent and intense negative emotions such as anger, fear, distress
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Positive and negative emotions can function independently and they need to be measured separately
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Sociability refers to the degree to which the person seeks to interact with others and to be with people
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It refers to stable individual differences on a dimension that ranges from hyperactivity to extreme inactivity
Activity may be defined with regard both to the vigor or intensity of responses and their tempo or speed
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But this may be faulty bc the mothers may have been influenced by their own expectations
Still tho - these results are so consistent that there must be a genetic significance
On the dimension of emotionality, identical twins are rated as much more similar by their mothers than are fraternal twins
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Conclusion: 1/3 - 1/2 of individual differences in temperamental traits can be attributed to genetic variation among children
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Degree to which the child's behaviour is inhibited
Shyness
Activity level
Empathy
Characteristics with genetic influence
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IN FOCUS 5.2 inhibited children: kagan's shyness research
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A notable example of research on temperaments that goes much beyond self-reports comes from jerome kagan's long-term research on inhibition and
shyness
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Kagan argues that inhibition is one of the major dimensions of temperament, and finds early individual differences exist on t his dimension and endure in the
course of development
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The highly reactive children showed greater fearful behaviour, heart acceleration, and higher blood pressure when they were p ut in an unfamiliar situation
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In short, temperamental differences in inhibition emerged as early as 4 months, were stable across the first 4 years of life, and showed moderate
heritability, suggesting a biological-genetic component in its development
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Can still change tho - inhibited infants grew up to be less inhibited preschoolers if they had mothers who were not overly protective and placed rea sonable
demands on them
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Attitudes and beliefs
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A substantial genetic influence was found on traditionalism - a general orientation that taps conservative (as opposed to liberal) attitudes on diverse topics
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A study found that the more heritable attitudes were harder to influence and also more important in determining the person's judgements of interpersonal
attraction
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Heredity and personality
September-30-12
7:39 PM
Chapter 5 Page 1
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