Chapter 3: Biological Foundations
What is the Genetic Basis of Psychological
- Genetics: describes hair color, weight, height, traits that are inherited.
o also refers to turning genes “on and off”
- envrioment affects genes are expressed -> how they affect our behaviour thoughts and feelings
- Major development in biological revolution -> Human Genome project
o To map entire human genome (genetic material/blueprint)
Humans have only about 30k genes maybe only 20k
Geneticists are now mapping individual genomes to compare gene expression
Eventual goal -> to understand how genes and their variation affect health and
Understanding genes -> cure illnesses and diseases through gene manipulation
o Genome – determines if a cell will be a part of one organ or another
What proteins will be made etc
o Chromosomes – made of genes, condensed genetic material
Humans have 23 pairs. Half come from mom, half from dad
Made of DNA
All cells have same genetic material
o Gene – segment of DNA that codes for a certain protein
Genes affected by environment
E.g. a certain gene is expressed for color in the development of a butterflie’s
wings depending on the surrounding temperature
Gene expression is not only physical characteristics but also involved in
psychological activity and development throughout life; allows us to learn, fall in
love, and to sense.
Heredity Involves Passing Along Genes through Reproduction
- Gregor Mendal – discovered mechanism for heredity 1866
o Used method of selective breeding – controlled which pea plant mated with which plant
o Crossed white flower plant w/ purple flower pea plant
F1 = offspring completely white or completely purple
o Crossed offsprings by self pollination
F2 = 3:1 ratio, 75% purple 25% white
o Concluded genes have diff forms (alleles) some dominant, some recessive
o Purple : dominant, expressed even if heterozygous (PW) or homozygous dominant (PP) o White: recessive, expressed only if homozygous recessive (WW)
- Genotype and Phenotype
o Genotype: genetic constitution, (PW or WW or PP)
o Phenotype: observable characteristic based on genotype (white flower or purple)
Affected by environment. Eg. Height and skin color based on genes but affected
by height also affected by diet and skin color by amount of sunlight.
- Polygenic Effects
o Height, intelligence etc. -> polygenic traits (traits that have much variability)
Not just smart or dumb, but everything in between
Not just short or tall, but everything in between
o Expressed by many genes not just one dominant/recessive pairing
E.g. diff tones of skin color -> result of multiple genes + enviroment
Genotypic Variation Is Created by Sexual Reproduction
- Siblings differ in eye color, height, personality b/c they are both created with a diff genotype
from diff combination of sperm and egg
- Humans have 23 pairs of chromosomes, one pair is the sex chromosomes X and Y
o Males have XY
o Females have XX
- Gametes are haploid, contain half the chromosome number and are made through meiosis
which increases genetic variation
o When sperm and egg meet during fertilization, they make a zygote -> distinct genotype
o Zygote grows w/ cell division (mitosis)
- Cell division is the basis of growth and and development. Old cells die, new cells are created.
- Errors can occur during cell division – mutations – insignificant in somatic, good or bad in
o Provides selection advantage or disadvantage, adaptive or maladaptive.
o Can spread through gene pool if adaptation from mutation proves to be beneficial to
survival -> more reproduiction to pass on adaptation
o E.g. industrial melanism in peppered moths
o E.g. can lead to disease, sickle cell anemia caused by mutation, maladaptive but remain
in gene pool.
Is recessive so it only occurs if both parents have it.
Benefit: resistance to malaria. Those who have one gene of SCA enjoy benefits
Genes Affect Behaviour
- What factors make you more/less intelligent? Bold? Be able to read a map?
o Psychological traits influenced by interactions of genes and the environment (raised or
Behavioural genetics -> study of how environment and genes influence
- People don’t wana betold what they can/cant do is beyold their control – ie genes. o Easy to accept that genes control physical characteristics
o Can genes determine how smart someone is? When they will get divorced?
o Genes lay the groundwork for human traits
Analogy: humans are like undeveloped photos, picture already captured but the
way it displays is based on the process used to develop pic.
o Psychological scientists study ways that characterists are influenced by nature nurture
and the combination. – the way genes are expressed in the environment
- Behavioural Genetics Methods
o Diff b/w siblings to be expected b/c they usually don’t share identical
o External factors vary subtly
e.g. mum may have eaten diff foods during pregnancy
diff friends, teachers, experiences
o Difficult to know what causes similarity and differences in siblings who share same
genes and experiences
o Two studies used: twin and adoption studies
Twin studies – compare similarities b/w diff types of twins and determine
underlying genetic basis of specific traits
Monozygotic (identical) twins – from one zygote, split to two zygotes
and develop simultaneously.
o Have same genes in chromosomes
o Recent study -> may not be exactly same b/c of how mom and
dad genes are combined
Dizygotic (non identical) twins – two diff eggs developed same time.
Identical twins are more similar than fraternal b/c came from same cell
Identical twins may not be same b/c diff enviroments or random
o Resulting in diff phenotype
Adoption studies – compares similarity b/w biological and adopted siblings
They share same home env but diff genes
Same home – little influence on many traits e.g. personality
Conduct behavioural genetic study -> compare identical twins that were
separated and raised separately
Study by uni of Minnisota – 100 pair of identical&nonidentical twins,
some raised together some apart
o Examined characterists – intelligence, personality, well-being,
achievement, alienation, and aggression
o General finding: identicals tend to be very similar, even if raised
o “Jim twins” brothers sperated at birth, raised by diff families.
Both married someone named linda (diff ppl though) Divorced, married someone named betty (diff ppl)
Smoke same brand of cigs, drink same thing, same
height, same jobs, same car, same dog name.
how is this possible ->strong genetic influences shape
personality and behaviour
o critics say, most adopted twins raised in similar enviroments in
the study. Doesn’t explain:
oskar stohr and Jack Yufe – raised diff places, diff
in interview, worse similar clothes, similar manners,
similar interests and behaviour
critics say: similarities occur in ppl of same age just by
coincidence even if ppl life diff lives
o some evidence – twins raised apart are more similar than twins
b/c parents encourage individualism thus creating diff
enviroments for each twins
Heredity – transmission of traits from parents to kid through genes
Heritability – statistical estimate of genetic proportion of the variation
in a specific trait.
o Depends on variation, it’s a measure of overall difference w/I a
group of ppl with particular trait.
o E.g. how many Canadian women within a group vary in height?
o Used to determine how much variation in trait in related family.
o E.g. do sisters tend to be similar in height than unrelated?
o Refers to population not indivduals
o If a height has a heritability of 0.6, then 60% of height variation
o Estimates of heritability only refer to the extent ppl differ in
terms of genetic makeup of a trait.
Social and Environmental Contexts Influence Genetic Expression
- Avshalom Capsi – study of criminality in 1000 group of Newzealanders from birth to adulthood
o Collected info on their lives every few years to which factors predicted who became a
o Mistreated kids – more likely to become criminals, but not all, why?
o Enzyme Monoamine Oxidase (MAO) – gene that codes for MAO, two forms
Low lvls – high susceptibility for early childhood maltreatment
High lvls – low susceptibility for early childhood maltreatment
o Although only 1 in 8 w/ low MAO gene AND maltreated responsible for almost half the
crime in the group. o Example of nature and nurture affecting behaviour, in this they are inextricable
- Sandra Scarr – another study to show genes and social context interact to affect phenotype
o Env influence children but genes also influence what experience they receive
E.g. if a kid is made fun of, either he shrugs it off, fights, or just walks away
This affects what environment they will be in
E.g. if a kid likes to read, the will stay indoors more and read more often then
someone who doesn’t like reading. This env is diff than someone who likes
outdoor activities and that kid will receive diff environmental experinces.
o Separating effects of social contexts and genes is impossible b/c they interact
Genetic Expression Can be modified
- Genes can be manipulated – enhance or reduce particular gene expression
o Insertion of genes from one animal to embryos of another animal also possible
E.g. a social vole gene put into antisocial mouse showed social vole behaviour.
o Allows comparison w/ unmodified to test theories of genes’ functions.
o If a gene is imp for a function and is “knocked out” (removed) – interferes specific
o Changing 1 gene can result in complete change in behaviour
o If a gene is knocked out, other genes may be expressed that weren’t previously
o Genes rarely work alone, they work together to make human complexity and experience
How Does the Nervous System Operate?
Neurons are specialized for communication
- Neurons – basic unit, excitable cell of nervous system. Operate and communicate w/ other
neurons through electrical and chemical signals
- Types of neurons
o Sensory (aka afferent) neurons – detect info from physical world through nerves from
muscles (somatosensory) -> send electrical signal through spinal cord -> sensory
o Motor (aka efferent) neurons – tells muscles to contract and relax, signal from brain to
o Interneurons – work as proxy, w/I a single area of body, to brain sensory neurons
o If you wanna use a pen, your brain sends signal to receptors in skin and muscle to move
in a way to pick up -> sends back signal to determine how much pressure is needed to
hold pen -> brain sends signal, to pick up with X pressure.
o Neurons don’t work randomly, they create circuits of neurons (neural networks)
o Neural commutations make our thoughts, emotions, every action. - Neruron structure
o Dendrite: short branchlike apendages that increase the neurons receptive field and
receive chemical signals
o Cell body: where info is received, collected and integrated from other neurons
o Axon: where electrical signals are transmitted along this long narrow thing
Longest axon from spinal cord -> big toe
Nerves refer to bundle of axons, carry info from brain -> other places in body
o Terminal Buttons: nodes at end of axons, neuron receive electrical signals -> release
chemicals to synapse(space b/w axon and dendrite) where chemicals communicate
o Chemicals go from axon -> dendrite-> cellbody
o Neuron membrane controls amount of ions that enter cell -> controls electrical charge
Signal goes down axon, insulated by myelin sheath (glial cell) fat substance
b/w sheaths called “nodes of ranvier” have ion channels that lets ions pass
through when neuron passes charge down axon
- The resting membrane potential is negatively charged
o When neuron resting, diff b/w electrical charge outside/inside called “resting
o Ratio of –ve to +ve ions greater inside than outside, outside more –ve
o Polarization : changing the charge inside/outside to generate electrical charge
- The roles of Sodium and potassium ions
o Na and K ions enter through ion channel in nodes of ranvier
o Specific channel for K ions and specific for Na ions
o When channel open, ions flow in, when closed, prevents inflow
o Polarization also caused by selectively permeable membrane
Causes more K ions inside than Na ions
Sodium – Potassium channels increase K in cell more than Na
Action potentials cause neural communication
o Action potential is electrical neural firing responsible for communication b/w neurons
- Changes in Electrical potential lead to action
o Neurons get chem signals from dendrites that tell to fire or not
o Two signals: excitatory and inhibitory
Excitatory: depolarize neuron: more likely to fire
Inhibitory: hyperpolarizes: less likely to fire
o If total amount of excitatory signal surpasses neuron threshold then it fires (action
o When neuron fires – Na channel opens, Na goes in making cell more +ve – K channel
opens, K leaves, cell becomes more +ve (all in cell membrane)
Change in charge is basis of action potential
o Na channel close – K channel close – charge returns into negative resting state. - Action potentials spread along axon
o Cell membranes depolarization moves along axon like a wave called propogation
o when neurons fire -> Na channel opens, causes adjacent Na channels to open. Domino
effect -> goes away from cellbody to terminal buttons ->action potential skips b/c of
ranvier -> pause briefly at each ranvier to recharge
o happens in 1/1000 second -> fast motor activity
o Multiple Sclerosis (MS) – neurological disorder, caused by deterioration of Myelin
Symptoms : blury vision, numbness in limbs
Deterioration of myelin slows down neural impulses, and exposes axon to be
Axons shortcircut and imterupts neural communications
Eventually loose motor control and develop jerky motion
MS common in cold climates and prevalent in ppl who grew up in cold
Not really ppl who move to cold. Dunno why
Genetic cause for MS? – more common in monozygotic twins and in females
- All-OR-None Principle
o Neurons get lots of excitatory and inhibitory signals
o Action potential only generated if the sum of these signals reach neuron +ve charge
threshold, ie. It depends on frequency of signals received
o All or nothing: neuron fires or it doesn’t, cant measure if strong or weak fire.
o How often it fires depends of strength of simulation ie. How fast you gona send signals
E.g. you look at bright light, you get more signals than if you look at dim light for
neurons in visual system
Neurotransmitters bind to receptors across the synapse
- Action potential causes release of neurotransmittors from terminal butons
o Travel from button -> dendrite in next neuron
o Neuron that sends signal (presynaptic) receives signal (postsynaptic neuron)
o Each terminal button has vesicles that contain neurotransmitters (communication
chemicals that carry signals)
o Action potential causes release of neurotranmittor -> received and binded to/by
receptor protiens on dendrite of postsynaptic neuron that cause excitatory/inhibitory
- Neurotransmitters Bind with Specific receptors
o each neurotransmitter has its own receptor protein-> influence
o Transmitters continue to release in synapse until terminated.
3 events that terminate transmitters’ influence in the synapse Reuptake: transmitters taken back into presynaptic terminal to be recycled.
Cycle of reuptake->release happens continuously
Enzyme Deactivation: specific enzymes destroy excess transmitters in synapse
Autoreception: monitor how much transmitter is released, if too much,
autoreceptor protiens signal presynaptic neuron to stop release.
o Same transmitter can generate excitatory or inhibitory proteins.
Neurotransmitters influence mind and behaviour
- Drugs can alter neurotransmittors