Psych 301, 10/20/3
Genetic and Biological Foundations
The genetic basis of psychological science
Basic concepts in genetics
DNA
Macromolecule built from nucleotides
4 types of nucleotide (A,C,T,G) allow for coding
Chromosomes
Strands of DNA
Present in pairs, one from each parent
Gene
Segment of chromosome
Basic unit of functionality
Allele
Sequence of nucleotides comprising a gene
Provides blueprint for creation of proteins, via RNA
Genetics and heredity
Genotype
Genetic “fingerprint” of individual
sequence of nucleotides in chromosomes
choice of allele for each gene
Same sequence in every cell
Determined at conception
Phenotype
Observable physical characteristics
Result of both genetic & environmental influences
Combined effect of both alleles for each gene
Dominant allele: Expressed in offspring whenever present
Recessive allele: Expressed only when matched with a similar recessive gene from other parent
Homozygous: Same allele on both chromosomes
Heterozygous: Mismatching alleles
Same phenotype as homozygous-dominant
Polygenic traits
Characteristics resulting from the influence of many genes, as well as the environment
Far more common that monogenic traits
Height, extraversion, intelligence...
Genotypic variation through sexual reproduction
Meiosis
Cell splits in half* to produce 2 gametes
Gametes (sperm/ova): cells containing only one of each chromosome pair (at random)
Zygote: union of sperm and ovum, has full set of chromosomes, half from each parent
Meiosis explains differences among siblings--each has a random half of each parent’s chromosomes
223  223 = 8,388,6082 > 70 trillion combinations
Mitosis
Occurs repeatedly after zygote is created
Chromosomes duplicate and cell divides
Explains growth of individual
Mutations: errors in duplication process
Behavioral genetics
The study of gene-environment interaction
Behavioral genetics methods
Twin studies
Monozygotic twins: identical genetic structure
Dizygotic twins: same genetic similarity as other siblings
Adoption Studies: Raised together vs. raised apart
Twin-adoption studies
Heritability
Estimate of how much variation in a trait is due to genetics vs. environment
Variance due to genetic factors divided by total variance in population
total variance = genetic variance + environmental variance
Property of the population in question
not a property of any one person
not inherent to the trait
differs across groups, depending on diversity
Operation of the nervous system
Neurons
Basic units of the nervous system
Specialized cells for internal communication and information processing
Receive, integrate, and transmit signals
Operate through electrical impulses
Communicate with other neurons through chemical signals
Parts of neurons
Dendrites: receive chemical signals from other cells
Cell body (or soma): collects and integrates inputs
Axon: transmits electrical signals (Action Potentials)
Terminal buttons: release chemical signals to other cells, in response to action potetials
Synapse: Site for chemical communication: terminal button of one cell and dendrite of another
Types of neurons
Sensory Neurons
carry incoming information from sensory organs, muscles (somatosensation)
afferent signals: environment affects brain
Interneurons
intermediate processing; responsible for everything but simplest reactions
vast majority of neurons in brain, ~100 billion
Motor Neurons
send commands to muscles
efferent signals: brain effects actions
Glial cells
Many support functions in brain
Guide development and migration of neurons
Provide structural support
Insulate axons (myelin sheath)
Waste removal
Smaller and more numerous than neurons (factor of 10)
Less well understood; May participate in information processing
Electrical properties of neurons
Membrane potential
Difference in electrical charge between inside and outside of neuron
Resting value approximately -70 mV
Maintained by sodium-potassium pump
Moves Na+ outside neuron
Moves K+ inside neuron (at 2/3 rate)
Ion channels in membrane
Selective permeability
Dependence on membrane potential
Transduction of incoming chemical signals
Chemical signals arriving at dendrites differ in effect on electrical potential
Excitatory signals
Lead to depolarization (potential moves towards zero)
Increase chance of action potential
Inhibitory signals
Lead to hyperpolarization (potential becomes more strongly negative)
Decrease chance of action potential
Action potentials
Electrical impulse passing along axon
Self-maintaining traveling wave, moves from soma to terminal buttons
Based on interactive dynamics of membrane potential and action of ion channels
Triggered by depolarization past threshold
Sodium channels open  Na+ rushes into cell  large positive potential
Positive potential forces K+ out of cell  negative potential re-established
Causes release of chemicals from terminal buttons
Properties of action potentials
Spatial and temporal summation
Absolute and relative refractory periods
Hyperpolarization following action potential
About 1 ms
All-or-none principle:
A neuron fires with the same potency each time
Cannot partially fire
Information is in frequency and timing of firing
Myelin Sheath
Fatty material made up of glial cells
Insulates the axon
Allows for rapid movement of electrical impulses along axon
10-fold increase in speed, up to 100m/s
Nodes of Ranvier: gaps in myelin sheath where action potentials are transmitted
Saltatory conduction: action potential jumps from node to node
Multiple sclerosis is a breakdown of myelin sheath