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Lecture 6

PSYB30 - Lecture 6.docx

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University of Toronto St. George
Elizabeth Page- Gould

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 can’t use this example anymore because there is more than one gene that controls 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 o Two alleles – one dominates o Also referred to as ‘mendelian inheritance’ • Codominance and incomplete dominance o Two alleles but neither is dominant, or one dominant – doesn’t hide effects 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 • Polygenic 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 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 Aparticular 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 Genotype Environment Positive High High Positive Low Low Negative High Low Negative Low High • Note: high or low indicates the amount of characteristic present in the genes or in the environment • 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 Behavioral Genetics • Attempt to determine % of individual differences in a trait due to genetic and % due to environment • Alot of research done in the area of intelligence – are infants born with a propensity to develop a certain level of intelligence, are there environmental components that can aid in intelligence – how much is it genetics, how much is it environment? • 99.9 behavioral factors (attitudes, behaviours, tendencies, etc.) in people is a combination of genetics and the environment • Determine the ways genes and environment interact and correlate to produce certain outcomes (individual differences) • Determine what relevant environment factors are such as parental behaviour, different teachers, learning activities, colours of walls in nursery, amount of lighting in nursery • Heritability: amount of observed individual difference in trait due to genetic differences. o What amount of differences in individuals can be traced back to differences in their genetic make-up • Environmentality: extent to which observed individual differences are due to environmental differences in individuals’lives Misconceptions about Heritability • Heritability CANNOT be applied to single individual o Only talks about population – looks at influence of genes and environment in a large group o Only applies to group-level variation o Only relevant to large groups • Heritability is NOT constant or immutable o Environment homogenous? - heritability higher = closer match between genotypes and phenotypes o Environmental variations increase - heritability will be lower = genotype has less of an impact of phenotype o Even highly heritable traits modifiable by environment • Heritability NOT a precise statistic – think estimate – can be a wide range estimate due to different methods, populations, samples(produces a range of heritability) • Ex. Intelligence ranges from 50% - 80% heritability Behavioral Genetics Methods • Selective Breeding—Studies of Humans’Best Friend, mice, rats • Family Studies • Twin Studies • Adoption Studies Selective Breeding • Can only occur if a desired trait is heritable (highly heritable) • Done using animals • Mate animals with desired traits until 100% of offspring have the desired trait • For example, miniature dog versions of larger dogs = normal versions selectively bred to produce miniature versions • Ex: depressed mice o You can breed mice to be depressed o Marker of depression – how much time the mouse spends struggling in a beaker of water before it gives up; mice that give up faster are depressed o With the desired product (offspring) can expose these offspring with this particular genotype to different environments o For example, can give depressed mice drugs that alleviate depression and see how much time each mouse spends struggling before they give up - do they take longer to give up • Can’t do this with humans because it is unethical • Mice are ideal because they reproduce quickly and in large quantities, can be easily bought, they are identical – don’t need to worry about variation • With humans have to use family studies, twin studies, and adoption studies Family Studies • Correlates degree of genetic overlap among family members with similarity in trait • Example: sensation seeking o Those high in sensation seeking will do more risky things, will go sky-diving, want to do activities that are more stimulating, lots of sound and colour, immersive experiences, dangerous activities o You have a measure of sensation seeking and you give it to all members of a family – look the relationship between how genetically similar individuals are and how similar they are in sensation seeking o If you argue that sensation seeking is highly heritable – you should see that parents and child are more similar in sensation seeking compared to first cousins, second cousins, etc. & first cousins more similar in sensation seeking compared to second cousins • Alot of correlational work involved • If trait is highly heritable, those more closely related should be more similar on the trait • Problem: Members of a family share elements of the environment—confounds genetic with environmental influences – it’s hard to tease them apart and see which aspect is actually having the effect • This is very difficult for extended families who are surrounded by the same environment • Thus, family studies never definitive – must do other studies as well • Therefore, must combine studies with different limitations – this way limitations will balance eac
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