PSB-2000 Lecture Notes - Lecture 2: Districts And Llgs Of Papua New Guinea, Twin, Twin Study

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PSB2000 Exam 1 Lecture Summary C. Robison Instructor
Lecture 2: Genes and Behavior
It is evident that a great deal of an animal’s behavior (including that of humans)
is dependent upon genetic factors. This is because genes code for proteins,
which determine the function of cells. The function of neurons in the CNS is what
determines behavior. Therefore, genes in*uence behavior but do not directly
cause
it.
Basic Genetics
Behavior is adaptive. Behaviors persist because they helped our ancestors
survive.
oThose ancestors passed on their genes to us.
oThose shared genes shape and otherwise in*uence our brains.
Genes are stored as DNA in the nucleus of our cells.
oDNA is bundled into units called chromosomes.
oDNA codes for proteins – complex “workhorse” biomolecules inside
our cells.
oThe DNA must be transcribed into copies of RNA molecules, which
go outside of the nucleus.
oThese RNA templates are then translated into proteins.
You have two copies of each of your genes – one from mom and one for
dad.
oYou get one copy of each chromosome from each parent.
If you have two copies of the same gene (i.e., mom and dad
both gave you the same gene), you are homozygous.
If the gene copies are di4erent, you are heterozygous.
oDominant traits are those that express in the heterozygous
condition.
Ex: if you have one gene copy for brown hair and one copy
for blond hair, you will have brown hair since the brown gene
is dominant.
oRecessive traits are those that express only in the homozygous
condition.
Ex: if you have blue eyes, you must have received a copy of
the blue-eyed gene from each parent because the blue gene
is recessive.
When DNA is transcribed to RNA, it is called gene expression.
When RNA is translated to protein, it is called protein expression.
Behavioral Genetics
You can tell if a behavioral trait is heritable (passed on through genes) by
observing its expression in families.
Twin studies are especially popular.
oExample: Examine identical versus fraternal twins.
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PSB2000 Exam 1 Lecture Summary C. Robison Instructor
Both identical and fraternal twins share the same
environment.
But identical twins have 100% of the same gene but fraternal
twins only have 50%.
Traits that are more correlated between identical twins
probably have a genetic component.
There are some confounding e4ects (systematic problems) in twin studies:
oShared prenatal environment may account for some of the
similarities.
oThe multiplier e4ect may amplify small initial behavior di4erences.
Some traits are sex-linked. This means the gene for that trait is located on
one of the sex chromosomes (usually the X chromosome).
oOne example is a form of red-green color-blindness.
Its gene is located on the X chromosome.
Females have 2 X chromosomes, so they are only color-blind
if they have
two
copies on the gene – one on each X.
Males have only one X chromosome, so they are color-blind if
they have
one
copy of the gene, since they only get one copy
via the X.
Some genes are sex-limited. These genes are present in both sexes but
require something that is present in only one of the sexes.
oFor example, the genes for baldness can be present in both males
and females.
oBaldness requires high circulating testosterone.
oSince females don’t have high testosterone, they don’t develop
baldness, even if they have the gene.
Epigenetics
Ultimately, it is gene expression that determines the heritability of traits.
You can change gene expression by making DNA more or less accessible.
oThis is called epigenetics.
One example is high licking and grooming (HLG) versus low licking and
grooming (LLG) rats.
oHLG rats have pups that grow up to be HLG and LLG rats have LLG
pups.
oIf you take a pup from an LLG mother and give it to an HLG mother,
she will grow up to be HLG.
But if you block epigenetics, you block this change and she will
be LLG just like her real mom.
Epigenetics is di4erent from genetics since there is no actual change to
the DNA, only how the DNA is accessed by the cell.
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PSB2000 Exam 1 Lecture Summary C. Robison Instructor
Lecture 3: Cells of the Nervous System
Cells are the basic building blocks of all tissues of the body, including the nervous
system. The cells of the nervous system can be broadly divided into two classes of
cells:
neurons
, the main signaling units of the nervous system, and
glia
, the main
support cells.
Introduction to Cells
All cells have several distinct internal structures called organelles. The
organelles include:
oThe
nucleus
, a membrane-enclosed area where the DNA is located.
The DNA is what codes for most of a cell’s biochemical properties.
oThe
cell membrane
, which keeps the inside of the cell separate from
the outside and controls the movement of molecules in and out.
oThe
mitochondria
, which act as the cell’s main fuel producers.
oThe
endoplasmic reticulum
which regulates the production and
transport of proteins.
Each type of cells (e.g. muscle, neuron, liver) is distinct because the DNA in
that cell expresses a certain subset of its genes.
oDi4erent genes = di4erent tissue types.
oThis causes di4erent cell types to be shaped and behave di4erently.
The
cell membrane
controls the transport of ions.
oOnly small, chargeless molecules (e.g., water and oxygen) can pass
the membrane without help.
oIons are charged and need the help of special
ion channels
in the cell
membrane to cross.
Sodium (Na+), Potassium (K+), Chloride (Cl-), and Calcium
(Ca2+) ion movement is important to the function of all cells,
especially
neurons.
Neurons
Neurons are the cells responsible for conducting signals and processing info
in the nervous system (NS).
oThey receive signals from other cells, process the info, and relay their
signals to other areas.
There are many di4erent subtypes of neurons.
oThey are categorized by their size, shape, neurotransmitters, and
membrane receptors.
oNeurons connect into networks to perform complex calculations.
In addition to the normal organelles, neurons have several special features.
oDendrites are long branchlike projections that get signals from other
neurons.
Dendrite means “tree” – they are shaped like branches.
They receive signals from the axon terminals of other neurons.
oSignals pass through the main body of the cell, called the soma.
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