nbd exam 1

What is genetics?

The study of genes, heredity, and genetic variation in living organisms.

What is Mendelian inheritance?

Inheritance of simple, single-gene traits in predictable patterns.

What is a monogenic trait?

A trait controlled by variation in a single gene or allele.

What is a polygenic trait?

A trait influenced by multiple genes.

What is pleiotropy?

When one gene influences multiple traits.

Polygenic vs pleiotropic?

Polygenic = many genes influence one trait; pleiotropic = one gene influences multiple traits.

What is the central dogma?

DNA → RNA → protein.

What is transcription?

Copying DNA information into messenger RNA (mRNA).

What is translation?

Using the code in mRNA to build amino acids/protein.

Where does translation occur?

At ribosomes; the lecture also emphasizes rough ER as a site of protein synthesis.

What does one codon specify?

One amino acid; a codon contains 3 nucleotides.

What initiates gene expression?

Regulatory DNA sequences such as promoters and enhancers/repressors, recognized by transcription factors.

What do transcription factors do?

Recognize regulatory DNA and help recruit the RNA polymerase complex.

What is the TATA box?

A key DNA sequence found in many promoters.

What does RNA polymerase do?

Synthesizes RNA using a DNA template.

What bases pair in DNA?

A pairs with T; G pairs with C.

What bonds link bases between opposite DNA strands?

Hydrogen bonds.

What bonds link nucleotides along one DNA strand?

Covalent phosphodiester bonds.

What does antiparallel mean for DNA?

The two DNA strands run in opposite 5′→3′ directions.

What is the shape of DNA?

A double helix.

What is an allele?

An alternative form of a gene.

What is homozygous?

Having two of the same alleles for a gene.

What is heterozygous?

Having two different alleles for a gene.

What is genotype?

The genetic makeup/set of genes an organism possesses.

What is phenotype?

Observable traits resulting from genotype plus environment.

What is penetrance?

The percentage of individuals with a given genotype who express the associated phenotype.

What is a dominant allele?

An allele expressed when present in one or two copies.

What is a recessive allele?

An allele expressed only when two recessive copies are present in the simple Mendelian model.

How can unaffected parents have an affected child in a recessive disorder?

Both can be unaffected carriers and each contribute a recessive disease allele.

Classic dominant disease example?

Huntington’s disease.

Classic recessive disease example?

PKU (phenylketonuria).

What is Huntington’s disease inheritance?

Dominant and nearly 100% penetrant in the lecture.

What brain areas degenerate in Huntington’s disease?

Basal ganglia and cortex.

What is phenotypic concordance?

The degree to which related individuals share the same phenotype.

What does less than 100% concordance in identical twins suggest?

Environmental/non-genetic influences also contribute.

Genetic similarity of monozygotic twins?

100%.

Genetic similarity of dizygotic twins?

About 50%.

What is cloning?

Creation of an organism that is an exact genetic copy of another.

Why are clones useful?

They help separate genetic from environmental influences.

What is a transgenic animal?

An animal with an introduced gene used to model a trait or disease.

What is a knockout model?

A model where a gene is replaced/inactivated to see what happens without its normal function.

What is a conditional knockout?

A gene can be turned off later after normal development to study its function in adults.

What is a SNP?

Single nucleotide polymorphism, a common one-base genetic marker.

Does a disease-associated SNP have to cause disease?

No. It may simply be near the causal gene.

What is recombination/crossing over?

Exchange/rearrangement of genetic material between homologous chromosomes during meiosis.

How does distance affect linkage?

Closer alleles are more likely to stay linked; farther alleles are more likely to be separated by recombination.

What can linked SNPs tell researchers?

They can provide a clue to the genomic location of a disease gene.

What does a LOD score measure?

The probability that two loci are linked rather than unlinked.

What LOD score supports linkage?

Greater than 3.

What LOD score argues against linkage?

About −2.

Major disadvantage of linkage studies?

Need many affected families across generations and are less useful for complex/polygenic traits.

Linkage vs association study?

Linkage tracks co-inheritance within families; association compares variants in unrelated individuals.

What structures make up the CNS?

Brain and spinal cord.

What is the PNS?

Nervous tissue outside the brain and spinal cord.

Basic flow through a neuron?

Dendrites → soma → axon hillock → axon → terminal buttons.

Main role of dendrites?

Receive incoming signals.

Main role of the axon hillock?

Sums postsynaptic potentials; if threshold is reached, an action potential is generated.

Main role of the axon?

Carries the action potential away from the soma.

Main role of terminal buttons?

Release neurotransmitter onto the next cell.

What does afferent mean?

Input arriving toward a neuron or region.

What does efferent mean?

Output leaving a neuron or region.

If A is presynaptic to B, how describe the flow?

A sends efferent output to B; B receives afferent input from A.

What do glial cells do?

Provide physical support, control nutrient flow, and participate in phagocytosis.

Approximate resting membrane potential?

About −70 mV.

Approximate threshold in the review figure?

About −55 mV.

At rest, where is Na+ more concentrated?

Outside the neuron.

At rest, where is K+ more concentrated?

Inside the neuron.

What two forces influence membrane potential?

Concentration gradient and electrical gradient.

What happens when Na+ enters?

Depolarization; the inside becomes less negative/more positive.

What happens when K+ leaves during an AP?

Repolarization.

Why does hyperpolarization occur?

K+ channels stay open/close slowly so extra K+ continues to leave.

Main AP phases?

Resting → depolarization → repolarization → hyperpolarization/undershoot → rest.

Which voltage-gated channel opens first in an AP?

Na+ channels.

How do voltage-gated Na+ channels behave?

Open fast and quickly inactivate.

How do voltage-gated K+ channels behave?

Open with a delay and stay open through repolarization.

What is the refractory period tied to?

Na+ channel inactivation is central; lingering K+ conductance contributes later.

What does all-or-none mean?

If threshold is reached, a full AP occurs; if not, no AP occurs.

What is saltatory conduction?

APs effectively jump between nodes of Ranvier on myelinated axons.

What are nodes of Ranvier?

Gaps in myelin where the AP is regenerated.

What is the synaptic cleft?

The small physical gap between pre- and postsynaptic membranes, about 20–30 nm in the lecture.

Presynaptic means?

Sending side.

Postsynaptic means?

Receiving side.

What is an axodendritic synapse?

Axon terminal contacting a dendrite.

What is an axosomatic synapse?

Axon terminal contacting a soma/cell body.

What is an axoaxonic synapse?

Axon terminal contacting another axon.

Sequence of neurotransmitter release?

AP arrives → Ca2+ enters presynaptic terminal → vesicles fuse → NT released → NT crosses cleft → binds postsynaptic receptor → PSP.

What ion triggers vesicle fusion and NT release?

Ca2+.

What is an EPSP?

Excitatory postsynaptic potential; graded depolarization moving closer to threshold.

What is an IPSP?

Inhibitory postsynaptic potential; graded hyperpolarization moving farther from threshold.

Classic EPSP ion movement?

Na+ influx.

Classic IPSP ion movement?

Cl− influx; K+ efflux can also hyperpolarize.

EPSP vs action potential?

EPSP is graded and can summate; AP is all-or-none after threshold.

What is spatial summation?

PSPs from different synapses/locations add together when they overlap in time.

What is temporal summation?

Repeated PSPs from the same input occur close together in time and add.

Where are EPSPs and IPSPs summed?

Axon hillock.

What is an ionotropic receptor?

A direct, fast receptor: NT binding directly opens an ion channel.

What is a metabotropic receptor?

An indirect receptor that signals through G proteins/second messengers.

Ionotropic vs metabotropic?

Ionotropic = direct/fast; metabotropic = indirect/more steps.

What is a ligand-gated channel?

A channel opened by ligand/neurotransmitter binding.

What is a voltage-gated channel?

A channel opened by a change in membrane voltage.