Week 3: Genetics and Evolution

Question 1

Nature-Nuture as a “debate”

Answer 1

So much controversy over this question - we are so concerned w nature/nurture because our very sense of moral character seems to depend on it

Born with certain characteristics while others are acquired

How do you set up an experiment to answer this question?

In typical human families, children’s biological parents raise them, so it’s difficult to know whether children act like their parents due to genetic (nature) or environmental (nurture) reasons

We see real-world examples of nature/nurture at work in the human sphere, though they only provide partial answers to our many questions

Question 2

Behavioural Genetics

Answer 2

Empirical science of how genes & environments combine to generate behaviour

Easiest opportunity to observe this is the adoption study

Question 3

Adoption Study

Answer 3

Behaviour genetic research method that involves comparison of adopted children to their adoptive and biological parents

Question 4

Twin Studies

Answer 4

Behaviour genetic research method that involves comparison of the similarity of identical (monozygotic; MZ) and fraternal (dizygotic; DZ) twins

Identical - Monozygotic; results from a single zygote (fertilized egg) and have same DNA; clones

Fraternal - Dizygotic; develops from two zygotes and share 50% of DNA; ordinary siblings who happen to have been born at the same time

Compare similarity of MZ and DZ pairs to analyze nature/nurture

Question 5

Quantitative Genetics

Answer 5

Scientific & mathematical methods for inferring genetic & environmental processes based on the degree of genetic and environmental similarity among organisms

scientific discipline in which similarities among individuals are analyzed based on how biologically related they are

Twin/adoption studies are two instances of a much broader class of methods for observing nature/nurture called quantitative genetics

Question 6

Heritability coefficient

Answer 6

An easily misinterpreted statistical construct that purports to measure the role of genetics in the explanation of differences among individual

Varying from 0-1, meant to provide a single measure of genetics’ influence of a trait; measures how strongly differences among individuals are related to differences among their genes

deceptively difficult to interpret

Question 7

You can’t leave… out of the equation

Answer 7

you can’t leave GENES out of the equation

Best predictors of an adopted child’s personaility/mental health are found in BIO parents they have never met, rather than the adoptive parents who raised them - presents a significant challenge to purely environmental explanations of personality or psychopathology

*No behavioural traits are completely inherited, can’t leave environment out all together

“Correlation doesn’t equal causation” - genetic AS WELL AS environmental

Question 7

Behaviorism

Answer 7

middle of 20th century, psych was dominated by doctrine of behaviourism - behaviour could only be explained in terms of environmental factors; neither behaviourism nor psychoanalysis is in compatible w genetic influences on behaviour, neither Freud/skinner was naive abt importance of organic processes in behaviour

Back in the day, it was widely though children’s personalities were shaped entirely by imitating their parents’ behaviour and that schizophrenia was caused by certain kinds of “pathological mothering”

Question 8

More-to-less genetic traits

Answer 8

Inability to organize traits from more to less genetic; everything has turned out to be at least SOMEWHAT heritable, yet nothing ABSOLUTELY heritable; not much consistency as to which traits are more heritable than others

Problem: heritability coefficient (and the whole quantitative structure that underlies it) doesn’t match up w our nature/nurture intuitions

Genes and environment are crucial to EVERY trait; the cause of a given trait depends not only on the trait itself, but also on the differences int hat trait between members of the group being studied

The heritability of a trait is not simply a property of that trait, but a property of the trait in a particular context of relevant genes/environmental factors

The science of nature and nurture has demonstrated that genetic differences among people are vital to human moral equality, freedom, and self-determination, not opposed to them

Question 9

Evolution

Answer 9

Change over time; certain traits and behaviours developing over time because they are advantageous to our survival

Question 10

Natural Selection

Answer 10

Differential reproductive success as a consequence of differences in heritable attributes

Reproductive success, not survival success, is the engine of evolution by natural selection

In order for our genes to endure over time we have inherited adaptive, psychological processes designed to ensure success

Question 11

Adaptations

Answer 11

Evolved solutions to problems that historically contributed to reproductive success

We can think of organisms as having two large classes of adaptations that evolved over time to increase our reproductive success

1. Survival adaptations - mechanisms that helped our ancestors handle the “hostile forces of nature”; sweat glands, shivering mechanisms, craving for fats/sugaras, fear to stay safe
2. Reproductive adaptations - help us compete for mates; described in evolutionary theory proposed by Charles Darwin - sexual selection theory

Question 12

Sexual Selection Theory

Answer 12

The evolution of characteristics because of the mating advantage they give organisms

Darwin noticed there were many traits/behaviours of organisms that couldn’t be explained by survival selection

two processes:
1. Intrasexual competition - members of one sex compete against each other, winner gets to mate w a member of the opposite sex; more attractive to potential maters increasing reproductive success; whatever qualities lead to success in intrasexual competition are then passed on w greater frequency due to association w greater mating success

2. Intersexual selection - members of one sex are attracted to certain qualities in mates (brilliant plumage, signs of good health, intelligence); desire qualities get passed on in greater numbers, simply bc their possessors mate more often

Question 13

Intrasexual v. Intersexual Competition

Answer 13

Intra - Process of sexual selection by which members of one sex compete w each other, and the victors gain preferential mating access to members of the opposite sex

Inter - process of sexual selection by which evolution occurs as a consequence of the mate preferences of one sex exerting selection pressure on members of the opposite sex

Question 14

Mutual Mate Choice

Answer 14

Unlike other animals, where one sex has dominant control over mate choice, humans have mutual mate choice

Both women and men typically have a say in choosing their mates; both value qualities such as kindness, intelligence, dependability that are beneficial to long term relationships - qualities that make good partners/parents

Question 15

Psychological Adaptations

Answer 15

Mechanisms of the mind that evolved to solve specific problems of survival or reproduction; conceptualized as info processing devices; in stark contrast to physiological adaptations (occur in body as a consequence of one’s environment); development or change of a mechanism in the mind

Ex. sexual jealousy - INPUT (romantic partner flirting w a rival); PROCEDURE (person evaluates the threat rival poses to romantic relationship); BEHAVIOURAL OUTPUT (might range from vigilance to violence)

Evolutionary psych focuses primarily on psycho adaptations

Wide ranging - food/habitat/mate preferences, specialized fears; research programs in evolutionary psych develop and empirically test predic=tions abt the nature of psycho adaptatoins

Question 15

Gene Selection Theory

Answer 15

Genes - basic units of heredity; info that is passed along in DNA that tells cells and molecules how to “build” the organism and how that organism should behave

Geens are better able to encourage organism to reproduce, thus replicate themselves in the organism’s offspring, having an advantage over competing genes that are less able

Genes can boost their own replicative success in 2 basic ways:
1. Influence odds for survival and reproduction of the organism they are in
2. Influence the organism to help other organisms who also likely contain those genes (“genetic relatives”) to survive/reproduce (called inclusive fitness)

Understanding gene replication is key to understanding modern evolutionary theory - fits well w many evolutionary psychological theories

Question 16

Evolutionary Psychology

Answer 16

fundamentally an INTERACTIONIST framework - theory that takes into account multiple factors when determining the outcome (an “interaction” between an environmental trigger and the initial response)

Culture has a major effect on pyscho adaptations

Evolutionary psych studies flexible, environmentally-connected and culturally-influenced adaptations that vary according to the situation

Question 17

Error Management Theory (EMT)

Answer 17

Deals w evolution of how we think, make decisions, and evaluate uncertain situations - situations where there’s no clear answer how we should behave

Cost asymmetries - choices w low cost but great reward or low reward but high cost

EMT predicts that whenever uncertain situations present us w a safer vs more dangerous decision, we will psychologically adapt to prefer choices that minimize the cost of errors

EMT is a general evolutionary psychological theory that can be applied to many different domains of our lives - Visual Descent Illusion, Auditory Looming Bias

EMT used to predict adaptive biases in domain of mating’ EMT predicts that men have a sexual over perception bias (often misread sexual interest from a woman); predicts men more than women will over infer sexual interest based on minimal cues, and empirical research confirms this adaptive mating bias

It’s important to consider how our evolutionary history has shaped our automatic or “Instinctual” desires and reflexes of today so that we can better shape them for the future ahead

Question 18

Visual Descent Illusion & Auditory Looming Bias

Answer 18

VDI - States that people will overestimate the distance when looking down from a height (compared to looking up) so that people will be especially wary of falling from great heights - would result in injury/death

ALB - people overestimate how close objects are when the sound is moving toward them compared to when it is moving away from them - if we think that a threat is closer to us when it’s moving toward us (bc it seems louder) we will be quicker to act/escape

Question 19

Gene

Answer 19

A specific deoxyribonucleic acid (DNA) sequence that codes for a specific polypeptide or protein or an observable inherited trait

Question 20

Epigenetics

Answer 20

Study of heritable changes in gene expression or cellular phenotype caused by mechanisms other than changes in the underlying DNA sequence; epigenetic marks include covalent DNA modifications and posttranslational histone modifications

Epigenetics has the potential to provide answers to important questions abt integrating findings from genetics/environmental factors into the study of personality/understanding emergence of mental illness; refers to the transmission of PHENOTYPE in terms of gene expression in the absence of changes in DNA

the examination of genetic-epigenetic-environment interactions from a developmental perspective may determine the nature of gene misregulation in psychological disorders

Question 21

Phenotype

Answer 21

Pattern of expression of the geneotype or the magnitude or extent to which it is observablly expressed - an observable characteristic or trait of an organism (ex. its morphology, development, biochemical/physiological properties, behaviour)

Question 22

Epigenome

Answer 22

Genome-wide distribution of epigenetic marks

Advent of high-throughout techniques such as sequencing-based approaches to study distributions of regulators of gene expression through the genome led to the collective description of the “epigenome”

Epigenome is highly dynamic, differing among cell types, tissues, and brain regions

Question 23

Identical Twins

Answer 23

Two individual organisms that originated from the same zygote & therefore are genetically identical/very similar; epigenetic profiling of identical twins discordant for disease is a unique experimental design as it eliminates the DNA sequence, age, and sex differences from consideration

Identical twins share a common GENOTYPE & are genetically identical & epigenetically similar when they’re young, but as they age they become more dissimilar in their epigenetic patterns and often display behavioural, personality, or even physical differences, & have different risk levels for serious illness - understanding the structure of the nucleosome is key to understanding the precise/stable control of gene expression/regulation, providing a molecular interface between genes/environmentally induced changes in cellular activity

Question 24

Genotype

Answer 24

the DNA content of a cell’s nucleus, whether a trait is externally observable or not

Question 25

DNA Methylation

Answer 25

Covalent modifications of mamalian DNA occuring via the methylation of cytosine, typically in the context of the CpG dinucleotide; cytosines followed by guanines, to form 5-methylcytosine in a cell-specific pattern

Enzymes that perform DNA methylation are called DNA METHYLTRANSFERASES (DNMTS)

Best understood epigentic modification influencing gene expression

DNA is composed of four types of naturally occurring nitrogenous bases: Adenine (A), thymine (T), Guanine (G), cytosine (C)

DNA methylation is like putting a lock on a recipe in your DNA book. It doesn’t change the recipe itself, but it can make it harder for your body to read and use that recipe. This process helps regulate which genes are used, and when, in different cells of your body.

Effect of DNA methylation on gene function varies depending on the period of development during which the methylation occurs/location of the methylated cytosine - methylation of DNa in gene regulatory regions (promoter/enhancer regions) usually results in gene silencing & reduced gene expression

INCREASED - gene silencing/tightening of chromatin
DECREASED - gene activation/loosening of chromatin

DNA methylation is a powerful regulatory mechanism that ensures genes are expressed ONLY when needed; may broadly impact human brain development, and age-related misregulation of DNA methylation is associated w molecular pathogenesis of neurodevelopmental disorders

Question 26

DNA Methyltransferases (DNMTs)

Answer 26

Enzymes that establish/maintain DNA methylation using methyl-group donor compounds or cofactors - the main mammalian DNMTs are DNMT1 (maintains methylation state across DNA replication), and DNMT3a and DNMT3b (Perform de novo methylation)

Catalyze the transfer of a methyl group to the cytosine; the enzymes are all expressed in the central nervous system & are dynamically regulated during development

Question 27

Histone Modifications

Answer 27

Posttranslational modifications of the N-terminal “tails” of histone proteins (chemical changes after the histone is made) that serve as a major mode of epigenetic regulation; these modifications include acetylation, phosphorylation, methylation, sumoylation, ubiquitination, and ADP-ribosylation; each of these modifications can act like signals that say “open this part of the DNA/close this part of the DNA” and can work together to regulate whether genes are turned on (to make proteins) or off (so they stay silent) - controlling gene activity w/o changing atual DNA = epigenetic regulation

Modification of histone proteins comprises an important epigenetic mark related to gene expression

Question 28

Histone Acetyltransferases (HATs) & Histone Deacetylases (HDACs)

Answer 28

HATs are enzymes that transfer acetyl groups to specific positions on histone trails, promoting an “open” chromatin state and transcriptional activation - HATs are like loosening the thread on the spool, making it easier to pull and read.

HDACs remove these acetyl groups resulting in a “closed” chromatin state and transcriptional repression - HDACs are like tightening the thread back onto the spool, making it harder to read.

In summary:

HATs = Add acetyl groups → Chromatin opens → Genes turn on
HDACs = Remove acetyl groups → Chromatin closes → Genes turn off

Question 29

Rats

Answer 29

In rats, increased amount of LICKING by the mother rat INCREASED the expression of the glucocorticoid receptor in the hippocampus (a brain structure associated with stress responsivity as well as learning and memory). This resulted in LOWERED hormonal response to stress compared with adult animals reared by mothers who engaged in lower levels of this behaviour.

Series of experiments w rats shows that histone acetylation/DNA methylation of the glucocorticoid receptor gene promoter is a necessary link in the process leading to the long-term physiological and behavioral sequelae of poor maternal care; points to a possible molecular target for treatments that may reverse or ameliorate the ttraces of childhood maltreatment

Question 30

Child Nutrition and Epigenetics

Answer 30

Nutrients can reverse/change DNA methylation and histone modifications, thereby modifying the expression of critical genes associated w physiological and pathological processes (embryonic development, aging, carcinogenesis)

Nutrients can influence the epigenome either by directly inhibiting enzymes that catalyze DNA methylation/histone modifications, or by altering availability of substrates necessary for those enzymatic reactions

Early life nutrition has the potential to influence epigenetic programming in the brain not only during early development but also in adult life, modulating health throughout life

nutritional epigenetics has been viewed as an attractive tool to prevent pediatric developmental diseases and cancer, as well as to delay aging-associated processes.

Question 31

Epigentic Regulation of Learning/Memory

Answer 31

Epigentic mechanisms influence genomic activities in the brain to produce long term changes in synaptic signaling, organization, and morphology - in turn support learning & memory

Question 32

Rett Syndrome

Answer 32

Patients have a mutation in their DNA sequence in a gene called MECP2 - plays many important roles within the cell (one role is read DNA sequence, checking for DNA methylation, and to bind to areas that contain methylation, preventing the wrong proteins from being present)

MECP2 and DNA methylation work together to control how genes are used in brain cells. When MECP2 doesn’t function properly, this regulation is disrupted, leading to the brain development and cognitive problems seen in Rett syndrom

Question 33

Rubinstein-Taybi Syndrome (RTS)

Answer 33

RTS patients have a mutation in their DNA sequence in a gene called CBP. One of these roles of CBP is to bind to specific histones and promote histone acetylation, thereby PROMOTING gene expression, and learning and memory

Consistent with this function, RTS patients exhibit a genome-wide DECREASE in histone acetylation and cognitive dysfunction (problems w learning/memory/brain development) in adulthood

In simpler terms, when CBP doesn’t work, the brain can’t make the proteins it needs for learning, memory, and growing new brain cells, leading to the cognitive challenges seen in RTS.