Ch. 4: Genetics, Evolution, Development, Plasticity Flashcards
Mendel
demonstrated inheritance occurs through genes
Genes
units of heredity that maintain structural identity
Chromosomes
strands of genes that come in pairs
DNA: Deoxyribonucleic acid
composed of genes
Strand of DNA serves as template model for
ribonucleic acid (RNA) molecules, a single-strand chemical. One type of RNA molecule—messenger RNA— serves as a template for the synthesis of protein molecules.
DNA has 4 bases
- Adenine
- Guanine
- Cytosine
- Thymine
The order of those bases determines the order of corresponding bases along an RNA molecule—adenine, guanine, cytosine, and uracil (in RNA and not DNA). The order of bases along an RNA mole- cule in turn determines the order of amino acids that compose a protein.
Some proteins serve as enzymes
catalysts that regulate chemical reactions in the body
Homozygous
same genes on your two copies of some chromosome
Heterozygous
an unmatched pair of genes
Dominant gene
shows a strong effect in either the homozygous or heterozygous condition
Recessive gene
shows its effects only in the homozygous condition
Can single gene produce particular outcome
No
Sex linked genes
The genes on the sex chromosomes (designated X and Y in mammals)
Autosomal genes
All other chromosomes are autosomal chromosomes and their genes are
You express most of your genes in certain cells and not others
changes in the environment can increase/decrease expression of a gene
RNA=
1 copy strand of DNA
Sex limited genes
present in both sexes but active mainly in one sex
Mutations
heritable change in a DNA molecule. Changing just one base in DNA to any of the other three types means that the mutant gene will code for a protein with a different amino acid at one location in the molecule.
Another kind of mutation is a duplication or deletion. During the process of reproduction, part of a chromosome that ordinarily appears once might instead appear twice or not at all. When this process happens to just a tiny portion of a chromosome, we call it a microduplication or microdele- tion.
Epigenetics
Changes in gene expression. Various experiences can turn a gene on or off. Epigenetic changes can be inherited for a generation or 2
Histones
Proteins that bind DNA. Histones tighten, stop expression of gene. If they relax, express gene. Adding methyl groups to a promoter turns off a gene
Difference b/w mutation and epigenetic change
A mutation is a permanent change in part of a chromosome. An epigenetic change is an increase or decrease in the activity of a gene or group of genes. Adding a methyl group turns genes off. An acetyl group loosens histone’s grip and increases gene activation
Heritability
If the variations in some characteristic depend largely on genetic differences, the characteristic has high heritability. Heritability ranges from zero, indicating no genetic contribution to the variation, to one, indicating complete control.
Monozygotic twins
Have the same genes. Not necessarily identical
Dizygotic twins
Don’t have same genes
Evidence of heritability
- Twin studies
- Children who have been adopted
- Candidate gene approach: Studies 1 gene
- Genome wide association study: Studies many genes b/w 2 distinct groups
Estimate of heritability of a trait
Specific to a pop at a given time
PKU
genetic inability to metabolize amino acid phenylalanine
Almost every human behavior
Has some degree of heritability
Evolution
Change over generations in frequencies of various genes in a pop
artificial selection
plant and animal breeders have long understood this idea, they choose individuals with a desired trait and make them the parents of the next generation
myth of Lamarckian evolution
use or disuse of some structure or behavior cause an evolutionary increase or decrease in that feature
Evolution depends on
reproduction, not survival
Evolutionary Psychology
How behaviors evolved
Kin selection
selection for a gene that benefits individual’s relatives
reciprocal altruism
Helping others with the intention of receiving help in return
group selection
altruistic groups thrive better
Homeobox genes
regulate expression of other genes and control start of anatomical development, like front and back directions
Process of development
- Fetus develops CNS at 2 weeks old
- Dorsal surface thickens, becomes tube and makes hind, mid and forebrain
- We start moving before receiving sensations
- Infant brain set up to see, hear, and receive sensory info but not how to interpret info (prefrontal cortex slowest to develop)
proliferation
production of new cells
Stem cells
Cells that do not become specified for some specific function, can become something else
When do most neurons form by
Most neurons form within first 28 weeks of gestation, process is stopped by premature birth
Early on primitive cells guided by
immunoglobulins and chemokines. Deficit in these chemicals leads to impaired migration, decreased brain size and retardation
Cell differentiates into
neuron, forms dendrites, axons and synapses (synaptogenesis, which begins long before birth but continues throughout life as neurons discard old synapses)
Myelination
glia produce fatty sheaths that accelerate transmission in vertebrate axons
What brain regions can generate new neurons
Hippocampus and olfactory bulb
Testing carbon in humans has taught us that
skin cells are produced rapidly, skeletal cells are 15 years old, hippocampus and basal ganglia (important for learning new tasks) generate new cells every year. Cortex doesn’t generate new cells
Growing axon follows chemical path based on
what is attracted to and doesn’t follow what it repelled from, leading to its appropriate destination
each postsynaptic cell
strengthens most appropriate synapses and eliminates others over time
Neural darwinism
in development of nervous system, we start w/ more neurons and synapses than we can keep, and then selection process keeps some of the synapses and rejects others. Most successful survive and others fail
Mutations in genes are
random events, but neurotrophins steer new axonal branches and synapses in approx. right direction
What determines how many axons survive
Muscles
Sympathetic nervous system first forms more neurons than it needs
When one of its neurons forms a synapse onto a muscle, that muscle delivers a protein called nerve growth factor (NGF), which promotes survival and growth of the axon
Axons that don’t receive nerve growth factor (NGF)
Degenerate and cell bodies die
Apoptosis
programmed mechanism of cell death. NGF cancels apoptosis
Loss of cells in a particular brain area often indicates
Maturation
Nerve growth factor is a neurotrophin
a chemical that promotes survival and activity of neurons. Essential for growth of axons and dendrites, formation of new synapses, and learning
fetal alcohol syndrome
Drinking into pregnancy can lead to thinning of cerebral cortex during adulthood
Brain neuron must receive input from incoming axons, alcohol inhibits receptors for
glutamate, brain’s main excitatory transmitter, and enhances receptors for GABA, main inhibitory transmitter
Sensory input instructs cortex about
how to develop
Far transfer
Idea that learning difficult skills will translate to general increase in ability. Has weak effect
Just as touch and sound come to activate what would be visual cortex in blind people
touch and vision come to activate what would be auditory cortex in deaf people
Competing hypotheses
practicing a skill reorganizes brain to maximize performance of skill. Other hypothesis is that brain characteristics present from birth lead people to a profession
proprioceptive training
bursts of vibration towards affected muscles
Teenage brain response to rewards is much stronger during teenage years
So risky behaviors reflects desire for excitement less than inability to inhibit impulse
Frontal cortex begins thinning at age
30
Closed head injury
injury that doesn’t puncture head
If a head injury causes confusion and loss of recent memory
Duration of this period is strong predictor of long term problems
stroke
cerebrovascular accident
Ischemia
Most common type of stroke. Result of blood clot/obstruction in artery
Hemorrhage
Less common, ruptured artery
Edema
Accumulation of fluid
Ischemia and hemorrhage
can lead to edema and dysfunction of sodium-potassium pump
Tissue plasminogen activator
Breaks up blood clots (P137). Only beneficial for ischemia, and can make hemorrhage worse. Hemorrhage is rare, so tPA often given at hospitals
Diaschisis
decreased activity in surviving neurons after damage to others
After cell loses input from an axon
it secretes neurotrophins that induce other axons to form new branches, or collateral sprouts, that take over vacant synapses (P139). If sprouting axons convey similar info as previous axons depends on their particular function
Denervation supersensitivity; receptor supersensitivity
When one set of synapses strengthen, the others weaken (and vice versa). Helps compensate for decreased input. Can strengthen desirable and undesirable connections, which can lead to things like chronic pain
If brain loses incoming axons
we can expect denervation supersensitivity, collateral sprouting, or both. Result is either increased response to a synapse that previously produced little effect, or response to an axon that previously didn’t attach at all
Phantom limb
Brain areas that start as particular body part continue to receive input even if body part is no longer there. Example: if axons representing face come to activate cortical area previously devoted to an amputated hand, touch on face produces facial sensation and sensation in phantom hand
Much recovery from brain damage depends on
learning to make better use of the abilities you were spared
deaferrented limb
Lost afferent sensory input
