PSY403: Genetics, Evolution and Methods (3.3, 4.1)

Genotype

hereditary info

typepheno

actual observed properties

genes

units of hereditary (pass down)

Chromosomes

strands of genes

-composed of DNA

DNA makes?

proteins

function of proteins

Make structures

-ex: receptors

-ex: protiens give neurons their structures

Control biological rxns

-enzymes are proteins

Homozygous

identical pair of genes on 2 chormosomes

heterozygous

unmatched pair of genes

dominant genes

effect in either homo or hetero condition

-one copy of gene is enough for trait to be expressed

-not more likely ot be passed down

Recessive genes

effects only in homozygous condition

-both genes have to match for trait to be expressed

example of: What do genes control sensitivity to?

taste of phenylthiocarbamide (PTC)

why isn't genetics simple

-many genes can contribute to one outcome

-genes can be expressed differently in diff parts of body

-genes can be expressed in some circumstances but not others

-behaviors in humans are usually a combo of genetic influences and environmental influences

Types of genetic changes

Mutation

Epigenetics

Mutation

heritable change in DNA

-change in DNA = change in function

Epigenetics

changes in gene expression without changing the DNA

-what protiens you make

How can epigenetic occur?

-some genes more active at certains of life (hair- gray hair)

-changes in gene expression are central to learning and memory

-experience can turn a gene on or off

-epigenetic differences are a likely explanation for differences btwn monozygotic "identical" twins

Heredity studies

Science is interested in how much can be explained by genes

-how heritable is a trait

-how much influence do genes have

Complex traits

show a combination of genetic and environmental influences

Methods for studying heritability

-Monozygotic vs. Dizygotic twins

-Adopted children

-Biochemical methods

How can twin studies help study heritability

-monozygotic twins: share genes

-Dizygotic twins: do not share more genes than other siblings

-If monozy twins show more similarity than dizygotic twins.. then...

how can adopted children studies help study heritability

-if adopted kids resemble biological parents, rather than parents who raised them...

how can biochemical methods help study heritability

-take samples from people, sequence a gene of interest, and see if the form of the gene they have predicts the behavior

How do genes affect behavior

-genes don't directly produce behaviors

-genes produce proteins that increase the probability that a behavior will develop under certain circumstances-genes can also have an indirect affect

how can genes have an indirect affect on behavior

genes can alter your environment by producing behaviors or traits that alter how people in your environment react to you

Evolution

change over generations in the frequencies of various genes in a population

Evolution of Behavior

-offspring generally resemble parents: trains can be passed on

-new genetic variations appear

-certain individuals reproduce more successfully than others, passing on their genes

What happens to genes that are associated with reproductive success

will become more prevalent in successive generation

Artificial Selection

Breeders choose plants or animals with desirable trait and make them parents of next generation

What does artificial selection require

-requires that variation exists

-req that trait is heritable

-breeder ensures taht some individuals reproduce more successfully

-gene becomes more prevalent with each generation

Who popularized natural selection

charles darwin

Natural selection

gradual process by which traits become more or less common in population as function of reproductive success

Different factors to measure in genetics research

-brain damage

-record activity during behavior

-correlate brain anatomy with behavior

Brain Damage Studies

-Broca

-Humans rarely have damage to just one area, and sit of lesion varies

-can be controlled in lab animals

-stereotaxic instrument

-TMS

Broca

Patient with damage to left frontal cortex

-lost ability to speak

-pattern across patients

-Brain damage can result in very specialized behavioral impairments

How to study brain damage in lab animals

-ablation: removal of brain area

-lesion: damage to brain area

Stereotaxic instrument

device precisely places electrode in brain

-anesthetize animal, drill hole in skull, insert electrode, put it into position, pass current to damage area

-sham lesion: everything but current

Transcranial magnetic stimulation (TMS)

Apply intense magnetic field to part of scalp, which temporarily inactivates neurons

-measure behavior before, during, and after stimulation

Example of how TMS can be used in a brain damage study

inactivate visual cortex

-no conscious perception of stimuli, but still have eye mvmts

How to record brain activity in animals?

insert electrodes and record activity

-there are also noninvasive methods

non invasive ways to record brain activity

-EEG

-MEG

-PET

-fMRI

EEG (electroencephalography)

electrical activity from brain recorded thru electrodes attached to scalp

-average activity of population of cells under electrode

-can record spontaneous activity or activity in response to stimulus

-can reveal info that behavior doesn't

EEG pros and con

-poor spatial resolution

-good temporal resolution

How can EEG have good temporal resolution

-millisecond by millisecond measurement

-electrical signal is direct measure of brain activity

How can EEG have poor spatial resolution

-over a population of cells

-scalp/skull/brain tissue can blur electrical signal (get in way)

-signal varies with coritcal depth and orientation of neurons

MEG (megnetoencephalography)

Measures tiny magnetic fields generated by brain activity

-magnetic field is less impacted by scalp

-better spatial resolution

PET (Positron Emission tomography)

Inject radioactive chemical used by brain, typically glucose

-as it decays, gamma rays are emitted

-scanner picks up on where those rays come from

-areas with most radiation are presumably area with most brain activity

fMRI (Functional magnetic resonance imaging)

measures changes in blood flow and oxygen content in blood

-scanner is strong magnet

-magnetic properties of blood let you see where brain is active

What shows in fMRI when brain area is more active

-more blood flow

-less oxygen in blood

Pros and cons of fMRI

-good spatial resolution (millimeters)

-poor temporal resolution

(hemodynamic response starts 1-2 s after neurons fire, and peaks after 6 s (note: neural responses are in milliseconds))

-MRI scanner is strong magnet ( limits who can use)

-Scanner is noisy and small

-You can't move

CAT (computerized axial tomography)

Head placed into scanner

-X rays sent thru head and recorded on opposite side

-scanner rotates aroundhead so that measurements taken at each angle

How do images appear on CAT scan

-dense structures (bone) appear white

-less dense materials (air) appears dark

-HYPERdense: brighter than brain

-HYPOdense: darker than brain

-gray adn white matter are more dense than CSF

-fat is less dense than water

-white matter has higher fat content (myelin) than gray, so it appears darker

MRI

uses powerful magnetic field (same machine as fMRI)

-tissues with different water content react differently to magnet

how much water in CSF, Gray matter, and White matter

-CSF: lots of water

-Gray: some water

-White: Least water (myelin)

DTI (Diffusion tensor imaging)

White matter connectivity

-Looks at direction of water mvmt

-water more easily flows down axon than across it

Describe color meanings of DTI

-Red: water moving left/right

-Green: water moving front/back

-Blue: water moving top/bottom