PSYC 3322 Ch. 4 Genetics, Evolution, Development, and Plasticity

Plasticity

changes rapidly in early development and continues changing throughout the lifetime (the brain's anatomy)

Genes and our environment are constantly

interacting with one another (an ongoing, complex interaction)

Mendelian Genetics

Gregor Mendel, late 19th century monk, demonstrated that inheritance occurs through genes

Genes

units of heredity that maintain their structural identity from one generation to another (come in pairs)

Genes are aligned along

chromosomes

Chromosomes

strands of genes (also come in pairs)

DNA

(the genes) double-stranded molecule, a strand serves as a template for the synthesis of RNA molecules

RNA molecules

single-stranded chemical

Messenger RNA

serves as a template for the synthesis of protein molecules

DNA consists of 4 bases:

adenine, guanine, cytosine, and thymine

Order of DNA bases determines...

RNA order of bases

RNA bases:

adenine, guanine, cytosine, uracil

Order of RNA bases determines...

the order of amino acids that compose a protein

Homozygous

identical pair of genes on the two chromosomes

Heterozygous

unmatched pair of genes

Genes are either dominant, recessive, or...

intermediate

Dominant (genes)

shows a strong effect in either homozygous or heterozygous condition

Recessive (genes)

shows effects only in the homozygous condition

Sex-linked genes

genes on the sex chromosomes (X and Y chromosomes in mammals)

Autosomal genes

all other chromosomes that are not sex-linked are autosomal with autosomal genes

Female (mammals) chromosome pair

XX

Males (mammals) chromosome pair

XY

Sex-limited genes

(autosomal chromosome) present in both sexes, but active mainly in one sex (ex. breast size in women, genes controlling chest hair in men), often show their effects in puberty, activated by sex hormones

Mutation

way in which a gene changes, a heritable, permanent change in a DNA molecule

Duplication/Deletion (type of mutation)

during reproduction, a part of a chromosome might instead appear once or not at all ("micro duplication /deletion")

Epigenetics

deals with changes in gene expression, helping us understand behavior

Which cells do not have DNA? (all but...)

red blood cells

Because of epigenetics people can...

have the same genes and environment but still turn out differently

Various experiences can do what to a gene?

turn it on or off (activities of genes can also vary)

Histones

proteins that bind DNA into shape

Epigenetic change

an increase or decrease in the activity of a gene or group of genes

Methyl group

adding this group, turns genes off

Acetyl group

loosens histone's (proteins that bind DNA) grip and increase gene activation

Heritability

estimate of the degree to which variation in a characteristic depends on genetic variations in a given population (genetics)

To determine heritability we rely on 3 kinds of evidence:

1. Compare monozygotic twins (identical)
2. Adopted children
3. Identify specific genes linked to some behavior

Comparing twins

monozygotic (one egg-identical), and dizygotic (2 eggs-fraternal, "virtual twins"- children of same age, adopted at the same time into a single family (same environment but no genetics)

Comparing adopted children

compare to biological parents (however, could indicate genetics, or prenatal environment)

Identifying genes linked to a behavior

ex. examine genes of a group of people with depression and compare it to the rest of the population

Environmental Modification

even highly heritable traits can be modified by environmental interventions ( heritable does not mean unmodifiable)

Phenylketonuria-PKU (example of environmental modification)

a genetic inability to metabolize phenylalanine (an amino acid)

How genes affect behavior:

in roundabout ways, may be direct or indirect (ex. brain chemicals vs. personality of an attractive woman)

Evolution

(proposed by Charles Darwin) a change over generations in the frequencies of various genes in a population (natural selection by the environment)

What do we know about Evolution?

offspring resemble parents (genetically), mutations/recombinations/microduplications introduce heritable variations that help or harm survival, some individuals reproduce more than others (passing on genes)

Artificial selection

process of selecting plants/animals with desirable traits (used to alter a species)

Fitness

the number of copies of one's genes that endure in later generations (more offspring that live=more fit)

Sexual selection

picking mates with the best genes in order to produce the best offspring (females usually choose males, ex. peacocks, because they have more invested) one-directional process, all below level of consciousness

Misunderstandings in evolution: (4)

1. Use/disuse of a structure does not alter increase/decrease of that feature in evolution
2. Humans have not stopped evolving
3. Evolution does not necessarily mean "improvement"
4. Evolution benefits genes (not species/individuals)

The only genes that we can pass on have to be present at

conception

Evolutionary psychology

concerns how behaviors have evolved (evolutionary + functional explanations)

Kin selection

selection for a gene that benefits the individual's relatives (ex. altruistic behavior in humans)

Proliferation

production of new cells (cells divide, some remain where they are continuing to divide-stem cells)

Vertebrates differ in proliferation by

number of cell divisions

Migration

early in development, primitive neurons move (varies in speed in direction, guided by chemicals: immunoglobulins and chemokines)

Differentiation

at first neurons, look like any other cell, then gradually differentiates, forming its axons and dendrites (axons first to destination, then dendrites form)

Myelination

(later and slower stage) process by which glia produce the insulating fatty sheaths that accelerate transmission in axons

Synaptogenesis

formation of synapses (final stage) begins at birth and continues throughout life (form new synapses and discard old ones)

New neurons later in life?

can be generated, exceptions include olfactory receptors because they are exposed to the outside world, also certain types of brain damage causes production

How to test for new neurons

use radioactive isotope carob 14C, cerebral cortex contains some amt. since birth, there should be few to no new neurons after birth

Pathfinding by axons

axons search for a specific target (ex. a muscle)

Sperry

he cut nerves, showing axon regeneration to original target (follows a chemical trail)

How an axon finds its target:

follows path of cell surface molecules attracted by some chemicals and repelled by others (steers direction)

Neural Darwinism

we start with more neurons and synapses than we keep, synapses form with accuracy then selection process keeps some and rejects others (only successful axons and combos survive)

Mutations in genes are...

random events

Neurotrophins

steer new axonal branches and synapses in the right direction, need for axon and dendrite growth, for the formation of synapses, and learning

Connections to target may be weak based on

experience (ex. lack thereof)

Determinants of Neuronal Survival

how matches occur, muscles send chemical messages to tell the sympathetic nervous system ganglion how many neurons to form (Rita Levi-Montacini confirmed)

Sympathetic nervous system (and neuron formation)

forms more neurons than it needs

NGF

sent to promote survival/growth (if no NGF the cell body dies if an axon does not make contact with appropriate postsynaptic cell-neuron kills itself)

Apoptosis

programmed cell death (neuron kills itself)

NGF is a neurotrophin:

chemical that promotes survival and activity of neurons (prevents apoptosis)

When do we have most of our neurons?

early life (*brain is most malleable and ready to learn in earliest development/youngest age)

Vulnerable developing brain

during early development the brain is highly vulnerable to malnutrition, toxic chemicals, and infections (ex. FAS in infants-babies are born with brain damage)

Fetal Alcohol Syndrome

alcohol consumption by mother, impairs neuron proliferation, migration, differentiation, and synaptic transmission (kills neurons), overstimulation at glutamate receptors can poison the mitochondria

Immature brain highly influenced by...

influence from the mother (ex. stress)

What is essential for the brain in early development?

stimulation and experience

Differentiation of the cortex

neurons differ in shape and chemistry

Ferret Study (differentiation of the cortex)

damaged one side of the brain, then trained to response to a stimuli on the normal side (turn one way to light, other way to sound), presented light to rewired side and responded/perceived light-determined that visual input to the auditory portion of the brain produced a visual sensation

Brains have ability to ______ themselves

remodel (in response to experience)

How long do dendritic branches remain flexible to change?

throughout the lifetime

What guides neuronal changes?

experience (ex. rats in enriched environment have more axons and dendrites, also more physical activity=more intellect)

Loss of a sensory causes

strengthened other sense through practice (ex. blind people use occipital lobe to help identify what they feel (sensory) and auditory info.), shown through scans and inactivation studies

Practicing a skill _________ the brain

reorganizes, to maximize performance of that skill (genetics may also play a role)

Brain and behavioral development in adolescents

frontal lobe is not fully development, prefer immediate rewards, more impulsive, weaker responses in prefrontal cortex responsible for inhibiting behaviors (highly responsive to social support and influence)

Brain and behavioral development in older age

memory and reasoning capabilities fade, loss of synapses and existing ones change slowly, may areas decline and decrease in size

Older adults compensate by: (3 ways)

1. Some may show little decline at all
2. They already have a basis of knowledge and experience
3. They may activate widespread brain areas (to compensate for deficiencies in 1 or 2 areas)

Causes of brain damage

tumors, infections, exposure to radiation, toxic substance, Alzheimer's, Parkinson's, closed head injury- sharp bow but no puncture (#1 in young people)

Stroke

(occurs mostly in older people) temporary interruption of normal blood flow to the brain ("cerebrovascular accident")

Neurons deprived of oxygen lose (during stroke)

oxygen and glucose supplies

Two kinds of stroke:

Ischemia and Hemorrhage

Ischemia

blood clot/obstructed artery

Hemorrhage

ruptured artery

Strokes (either ischemia or hemorrhage) can lead to...

Edema-pressure on the brain, puts a person at risk for additional strokes

What helps prevent damage after a stroke?

medications (ex.tPA- breaks up blood clots after stroke), decreasing stimulation by blocking glutamate synapses or blocking calcium entry (ALSO- "cool" brain and Cannabinoids)

Later mechanism of recovery after brain damage

damaged areas of the brain increase and reorganize their activity (another area takes over function of the damaged or some other form of compensation)

Increased brain stimulation- after damage areas that have lost normal input become

less active

Diaschisis

refers to the decreased activity of surviving neurons after damage to others (increased stimulation should help during a later period of recovery)

Where should stimulation therapy occur?

direct stimulation should be applied at cells that had been receiving input from the now damaged cells

Regrowth of axons

(limited in mammals-bc of scar tissue), neurons on each side pull apart and glia release chemicals that inhibit axon growth

What happens in the brain near damage?

synapses form at a high rate, areas that lost input secrete neurotrophins that induce other axons to from new branches

Collateral sprouting

damaged areas secrete neurotrophins (chemicals) which induce axons to form new branches in order to take over the vacant synapses (caused by damage)