PSYB30H3 Lecture Notes - Lecture 6: Gregor Mendel, Gene Expression, Behavioural Genetics

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20 Mar 2013
PSYB30 Lecture 6 Purple Text Prof’s Speech
Personality and Genetics
(Relevant) Cell biology basics
Cell nucleus contains DNA
DNA Carries genetic information (for all living things )
DNA Controls growth and development ; determines what someone will end up
looking like, determines how tall they will be; sets the blueprint for various aspects of
All living things have DNA
- Controls everything that they person will not be learning
- DNA is organized into chromosomes
23 pairs of chromosomes in humans
- every cell in the body has all 23 pairs of chromosomes
- DNA is divided into various chromosomes
- DNA and genes in a strand of DNA, the ―rungs of the ladder‖ are made up of
bases (C, G, T, A) the ordering of the letters is the genetic code which
determines if you will be a ―banana or a human being‖
One gene = 100 to several million pairs of bases/‖rungs of the ladder‖; a segment of the DNA
Gene expression: genotype vs phenotype
Genotype = specific genetic makeup
- Illustration/depiction of DNA; order of bases on DNA = genome, which
corresponds to genotype
- made up of alleles
o alleles gene variant
Phenotype = how genetic makeup is expressed
- what is seen; what comes out in the individual
- i.e. in eye colour blue eyes would be a phenotype
Forms of gene expression
Two alleles where one dominates and dominating gene will be expressed
Also referred to as Mendelian inheritance (after Gregor Mendel)
Codominance and incomplete dominance
Two alleles but neither is dominant, or one dominant - doesn’t hide effects of
Codominance: both expressed
See both of the genes (i.e. an offspring gets an allele for white hide
and brown hide = a cow that is half white and half brown)
Example: blood type A allele, B allele = dominant, O allele =
Incomplete dominance: combination expressed
i.e. Black and white cow mate to make grey offspring
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Most human traits, especially personality traits, are all polygenic
Many pairs of alleles create expression, more than one gene that is
responsible for that particular trait
Skin colour is polygenic
Role of Environment
=Genotype + environment -- phenotype consists of the independent effects of the genotype and
the environment
+gene-environment interaction – and also the interaction between the genotype and the
+gene-environment correlation
(with formulas, know what they mean, but will not have to calculate anything)
Genotype-Environment Interactions
Impact of environment depends on genotype – two people can encounter the same environmental
factors but they don’t react in the same way because of an interaction with their genotype
- Study in textbook – maternal rejection and genotype in depression
- Diathesis stress model – case where someone has a predisposition to develop a
condition or disorder
Example: Religious upbringing reduces influence of genetic factors on disinhibition (i.e.
partying, risk-taking, etc.)
- Study between genotype for disinhibition and religious upbringing
- If there was a religious upbringing, less likely to be disinhibited – had to do with
interaction between genes and environment
Genotype-Environment Correlation
Differential exposure of individuals with different genotypes to different environments
- People with different genotypes are exposed to different environments
- The impact of the environment depends on the person’s genotype
- With correlation – harder to separate genotype and environment because there is a
3 different ways that this works:
- Passive: Parents provide both genes and environment to children, child doesn’t
play a role
o Example: Child’s verbal ability and the number of books in home
Child shows good verbal ability, parents provide resources for the
child to improve on that ability
o Children don’t have anything to do with the environment they’re exposed
to, but they are exposed to it because of their genotype
- Reactive / evocative: Parents (or others) respond to children depending on the
o Child evokes certain reaction in parents or other caregivers
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