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Lecture 6

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University of Toronto Scarborough
Connie Boudens

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 development 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 • Dominant-recessive • 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 other • 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 = recessive • Incomplete dominance: combination expressed • i.e. Black and white cow mate to make grey offspring • Polygenic • 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 Phenotype =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 environment +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 correlation 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 genotype o Child evokes certain reaction in parents or other caregivers o People respond to different children differently depending on their genotype o Example: Baby’s liking for cuddling and mother’s cuddling behavior - Active: Person with particular genotype seeks out environment o When an infant gets old enough to choose environment o Example: High sensation seekers expose themselves to risky environments In general, Passive type decreases with age, active type increases because people become more mobile and have more control over their environment Genotype-environment correlations can be positive or negative - Positive: If someone has a certain genotype, they will wind up or choose to be exposed to environments that will enhance that genotype and lead to a greater likelihood that it will be expressed - Correlation can be negative: if someone has a particular genotype they might be exposed to an environment that discourages that genotype o i.e. a loud child with parents who don’t want him/her to be loud *know the difference between g-e interaction and g-e correlation Behavioural Genetics - behavioural genetics – area of research where people are trying to figure out what % of differences in a trait are due to genetic differences and what % are due to environmental differences Attempt to determine % of individual differences in a trait due to genetic and % due to environment Want to Determine the ways genes and environment interact and correlate to produce certain outcomes - particularly interested in outcomes that cause particular differences Also want to Determine what relevant env. factors are. – does it have to do with learning activities, parental behaviour, type of teachers, amount of light, colour of walls, etc. - 99.9% of behaviour factors is some combination of genetics and environment Heritability : amount of individual difference in trait due to genetic differences. Environmentality extent to which individual differences are due to environmental differences MisconceptionsAbout Heritability Heritability CANNOT be applied to single individual – talking about populations Only applies to group-level variation Technology is not at the point where you can look at the individual level yet Heritability NOT constant or immutable Environment homogenous? - heritability higher - For people who are in the same environment – higher match between genotypes and phenotypes, rate of heritability will be higher Environmental variations increase - heritability will be lower - As environmental variation increases, you will see less of an influence of the genotype on the phenotype Even highly heritable traits are modifiable by environment Heritability NOT a precise statistic – think estimate, sometimes the estimates have a wide range which is because different researchers use different methods, populations, etc. - Example: intelligence – range can be from 50-80% Behavioral Genetics Methods Selective Breeding—Studies of Humans’Best Friend Family Studies Twin Studies Adoption Studies Selective Breeding Can only occur if a desired trait is heritable Done using animals – look for animals that are exhibiting a particular b
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