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Lecture 6

PSYB30H3 Lecture Notes - Lecture 6: Sensation Seeking, Eye Color, Twin Study

Course Code
Lisa Fiksenbaum

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Personality & Genetics
Cell Biology Basics
Nucleus of cell contains all DNA
o DNA contains all genetic information for all living things
o DNA controls growth and development determines how someone will look, aspects of
personality, how tall person will be, blueprint for various other aspects of development
o All living things have DNA and DNA controls anything that is NOT learnt
o DNA is organized into chromosomes = humans have 23 pairs of chromosomes every
cell in your body has 23 pairs of chromosomes this contains all of your DNA
o Ordering of bases (A, T, C, G) = genetic code
One gene = segment of DNA = 100 to several million base pairs
Gene expression: genotype vs. phenotype
Genotype = specific genetic makeup
o Order of bases in gene
o Made up of all of the different alleles you have alleles are gene variants
o Not all of a genotype is always expressed
Phenotype = how genetic makeup is expressed
o What you actually see, what actually comes out in a person
Ex. Eye colour
o Can have genotype with combination recessive and dominant alleles
o Brown eyes = B
o Blue eyes = b
o You get one allele from each of your parents, depending on your combination
determines your eye colour
o But at use this eaple aore eause there is ore tha oe gee that otrols
eye colour
Ex. Characteristics of garden peas as discovered by Mendel (Father of Genetics)
o Seed shape, seed colour, flower colour, pod shape, pod colour
o Noticed that some characteristics would skip a generation and wondered why this was
o So he cross pollinated different plants to see what the outcome would be - from this he
came up with the idea of dominant and recessive traits
o In order to test theory of dominance and recessive traits he bred certain pea plants
specifically to show certain characteristics looked at F1 and F2 generations
o Dominant traits mask recessive traits, only when there are two recessive alleles does the
recessive trait show
Forms of Gene Expression
Dominant Recessive
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o Two alleles one dominates
o Also referred to as medelia iheritae
Codominance and incomplete dominance
o Two alleles but neither is dominant, or one dominant doest hide effets of other
o Codominance: both expressed
Ex. Brown cow and white cow mate offspring half brown and half white
Ex. Blood type: A and B alleles = dominant, O = recessive
AB = blood AB, AO = blood type A, BO = blood type B, OO = blood type O
o Incomplete dominance: combination expressed
Combination of two alleles is expressed
Ex. Black cow + white cow offspring = grey
Ex. Red flower + white flower offspring = pink
Ex. Skin colour
o Many pairs of alleles create expression
o Most human traits, especially personality traits are polygenic
o Many genes control a trait such as skin colour
Role of Environment how does the environment interact with genes to produce a certain outcome?
Phenotype type
o = genotype + environment
o +gene-environment interaction
o +gene-environment correlation
Genotype-environment interactions
o Impact of environment depends on genotype same environment but different
genotypes = different expressions in phenotype
o Two people can placed in the same environment stress, stimuli, opportunities but they
react differently due to different genotypes
o Example: religious upbringing reduce influence of genetic factors on disinhibition
In this study they looked genetics differences and similarities in disinhibition
(doing wild things partying, sexual risk taking, other risk taking, etc.)
They looked at people who could be argued to be similar or different for their
genotype on disinhibition and separated them according to if they had a
religious upbringing or not
Results: if you had genotype that would encourage disinhibition but were
brought up religiously disinhibition would not be fostered
However those with the genotype for disinhibition and no religious upbringing =
disinhibition expressed
People with religious upbringing less likely to be disinhibited = interaction
between genotype and environment
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Genotype-Environment Correlation
Differential exposure of individuals with different genotypes to different environments =
people with different genotypes are exposed to different environments
o People are exposed to different environments based on genotypes
o Harder to separate genotype from the environment because there is a correlation
between the genotype and the environment
Passive: Parents provide both genes and environment to children. child doesn’t play a
role (in obtaining the environment) because parents are providing both genetic aspects
and aspects of the environment
o Child’s verbal ability and the number of books in home
o If a child is showing very high verbal ability and the parents then provide various
resources to improve verbal abilities
Reactive / evocative: Parents (or others) respond to children depending on the genotype
o The child’s attributes evoke certain reactions – the child is evoking a certain
reaction in parents or other caregivers
o People respond to children differently based on genotype
o Ex. Baby’s liking for cuddling (genetically based liking for touching) and
mother’s cuddling behavior is evoked
Active: Person with particular genotype seeks out environment
o When an infant gets old enough to choose different elements of its environment
o A particular genotype causes you to be interested for different things in the
environment and causes you to look for different things in the environment
o Ex. High sensation seekers expose themselves to risky environments
o Ex. Child who doesn’t like to be with others will seek out opportunities to be
alone, child who likes the company of others will seek others company
Passive decreases with age, active increases due to better control and more mobility
individuals obtain
Genotype-environment correlations can be positive or negative
Type of Correlation
Note: high or low indicates the amount of characteristic present in the genes or in the
Negative correlation example: child is very loud boisterous (genotype high), parents
encourage the child to calm down, put the child in timeout, put the child in environments
that don’t encourage this behaviour (environment low)
Negative correlation example: child is very quiet (genotype low), parents encourage child
to be more outgoing and enroll them in classes (environment high)
Positive correlation people with certain genotypes end up in environments that foster
these genotypes and increase the expression of these genotypes
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