Chapter 3

Question 1

The neuron is a specialized cell & the —— of our nervous system

Answer 1

The building block

Question 2

What was Golgi’s rejected neuron theory?

Answer 2

• NS as an interconnected network of fibres with information flowing through it like water which led to behaviour
• Golgi’s “nerve net” confirmed as true, which is a covering called perineuronal net forming around neurons as they mature.

Question 3

What was Cajal’s neuron theory?

Answer 3

• NS is made up of discrete cells that begin as a simple structure–> become more complex with age
• The more neurons–> the more complex the behaviour
• When mature, these cells consist of main bodies with many extensions
• Glial cells which make up a large part of brain tissue are distinguishable from neurons
• Neurons are the functional units of NS and interactions between them enables behaviour

Question 4

What are the 3 parts of a neuron?

Answer 4

1) Dendrites “Greek for tree”–> branching extensions that collect info from other cells
2) Cell body/Soma “Greek for body”–> core region that integrates gathered info
3) Axon “Greek for axle”–> the main root that carries messages to other neurons

• Neurons have many dendrites but only one axon
• The human body has 86 billion neurons
• 1:1 ratio characterizes brains of all animals

Question 5

Describe how neurons process information:

Answer 5

• Neurons acquire information, store it as memory, interpret & pass it along to other neurons–> behaviour is produced & bodily processes are modulated
• Work in groups of hundreds/thousands
• NBD if a few neurons are lost & neuroplasticity compensates for it since they produce new branches, lose old ones and connect with each other dynamically
• Neurons have up to 20 dendrites, with 1 or many more branches and thousands of dedritic spines (small protrusions)
• The dendritic spines are the POC with the neurons
• The more branches & spines–> the more info processed

Question 6

Describe parts of an axon:

Answer 6

-A single axon carries messages to other neurons

• Begins at an expansion called axon hillock (little hill)
• May branch out into axon collaterals (emerge from it at right angles)
• Axon collaterals may divide into smaller end-branches called telodendrion
• At the end of telodendrions are terminal buttons (end foot)
• Buttons sit closely but do not touch the dendritic spine of another cell
• Create a synaptic connection (transfer site) that includes the surface of terminal buttons, and the neighbouring dendritic spine
• A lot of info is collected from many sources on a neuron’s dendrite but only a single message can be sent out by the axon over its collaterals & telodendrion

Question 7

What are the 3 specialized functions of neurons?

Answer 7

1) Sensory neurons (have many types) conduct info from sensory receptors into spinal cord & brain
2) Interneurons (multibranched) associate sensory & motor activity in CNS
3) Motor neurons (distinctively large) carry info from the brain & spinal cord out to the muscles

Question 8

Describe the different types of sensory neurons:

Answer 8

• Structurally, the simplest type of neuron
• Bipolar neurons–> transmit incoming sensory info from retina’s light receptors to neurons carrying info to the visual centers
• Somatosensory neuron–>
• A little more structurally complex.
• The dendrite connects directly to the axon & cell body sits on one side of the axon
• Bring sensory info from the body to the spinal cord.

Question 9

Describe the different types of interneurons:

Answer 9

• Also called association cells due to their linking of sensory & motor neurons
• Branch extensively & collect info from many sources
• There are more interneurons in larger brains than smaller ones–> one of the reasons for variation in brain size
• Stellate (star-shaped)–> (Think “Stella from Winx”)
• small, with many dendrites extending around the cell body

-Pyramidal cell–> (“Think Illuminati top of my head”)
-long axon, pyramid cell body & 2 sets of dendrites:
Apical set–>projecting from the cell body’s apex
Basal set–>projecting from the base of the cell body
-They carry info from cortex to rest of brain & spinal cord

Purkinje cell–> (Think “Big tree, small brain”)

• Extremely branched dendrites forming a fan shape
• Carries information from the cerebellum to the brain & spinal cord

Question 10

Describe motor neurons:

Answer 10

• Extensive dendritic networks, large cell bodies & long axons connecting to muscles
• All efferent neural info must pass through them to reach muscles
• Reside in lower brainstem & spinal cord

Question 11

How are neuronal networks formed?

Answer 11

1) Input
2) Association
3) Output

• Sensory neurons collect afferent info from the body–> connect to interneurons that process the info–> pass it on to motor neurons–> efferent connections move muscles
• Long-distance projecting neurons are relatively large (e.g somatosensory, pyramidal & motor neurons)
• If they have a large cell body, they have long extensions (carry info to distant parts of NS); small cell body (e.g stellate) have short extensions (local processing)
• Sensory neurons could send info as much as 2 meters or more
• Axons of some pyramidal neurons are even 1 meter long

Question 12

What is the role of neurons in excitation & inhibition?

Answer 12

• Yes signals are excitatory, no signals are inhibitory
• Each neuron receives thousands of signals per second
• Neurons respond to these signals by summing them
• A neuron whose excitatory inputs exceed its inhibitory inputs sends messages to other neurons
• A neuron whose inhibitory inputs exceed its excitatory inputs, the neuron will not communicate
• A neuronal network can detect sensory info and decide what kind of motor response to make to that info

Question 13

Describe the experiment with the robot that behaves like a cricket on the basis of neuronal excitation/inhibition:

Answer 13

• Sensory neurons from microphone excite motor neurons at the plus sign–>but input from photoreceptors inhibits them at minus sign
• Excitation inputs are picked up by the microphone–> activate the wheels at the plus sign–> orient toward the cricket’s chirping
• Anthripomimetic robots are being made to mimic human body parts for those with lost limbs

Question 14

What are 5 types of Glial cells?

Answer 14

Gliomas–>

• Arise from glial cells, are slow-growing, not often malignant & easy to treat if risen from astrocytes.
• Those arising from germinal cells that grow into glia are more malignant, rapid-growing & recur after treatment

Meningiomas–>(Think “Man Inja Am”)
-Attach to meninges, grow outside the brain & are encapsulated (contained), good recovery after surgery

Metastatic tumour–>(Think “Me too static??”)
-Establish after cells from one region transfer to another, present in multiple locations & symptoms present when they reach the brain. Difficult to treat

Astroglia Astrocytes (star-shaped glia) (Think “Astropolice”)

• Extensions attach to blood vessels & brain’s lining to hold neurons in place
• Provide structural support to CNS
• Provide pathways for nutrients to move between blood vessels & neurons
• Secrete chemicals that keep neurons healthy & help them heal
• They also enhance brain activity by increasing blood flow & fuel supply
• Form scars around injured areas of the brain but acts as a barrier for regrowth of damaged neurons
• Contribute to the blood-brain barrier by attaching their ends to blood vessels & causing them to bind tightly–> preventing toxins from entering the brain through vessel walls
• Many useful drugs (e.g antibiotics) cannot pass through which makes brain infections difficult to treat; medication must be tubed directly to the brain

Question 15

What are Ependymal cells?

Answer 15

• Fluid-filled cavities on the walls of the ventricles–> produce CSF that fills the ventricles–> flows toward the base of the brain & absorbed through blood vessels (Think “EPCY”)
• The CSF is a source of nutrients for adjacent areas to the ventricles & maintains the brain’s constant temperature
• If passages are blocked, CSF flow becomes restricted–>due to its constant production, blockage leads to pressure buildup–> expanding ventricles
• Hydrocephalus “water brain”–>
• Occurs when ventricles expand in a newborn infant before skull bones are fused, causing swelling
• Severe intellectual impairment & death
• Insert one end of a tube into a blocked ventricle and the other end into a vein to allow CSF to drain to the bloodstream

Question 16

What are Glial cells?

Answer 16

Glial cells–>

• Greek for “glue” is the NS support cells
• Don’t transmit info themselves but help modulate neuron’s activities by binding them together, providing support, nutrients & protection
• Most types of glial cells are produced throughout one’s life & replication errors lead to brain tumours (uncontrolled growth of new tissue independent of surrounding structures)
• Surgery is effective in treating tumours, chemotherapy less so because of blood-brain barrier blocking chemical inserts while radiation therapy has bad side effects for developing brains

Question 17

What are Microglia?

Answer 17

• Originate in the blood as opposed to other glial cells that originate in the brain
• An offshoot of the immune system that migrates in the NS & makes up 20% of all glial cells
• Do not enter the brain; they monitor & maintain the health of brain tissue by attacking foreign tissue
• Provide growth factors that support brain cell growth in damaged cells & interact with astrocytes in healing
• Engulf foreign tissue & dead brain cells through phagocytosis–> turn into stuffed, no-longer functioning dark bodies near damaged regions
• Could become harmful if they consume inflamed tissue instead of protecting it
• Alzheimer patients deposit plaques near damaged regions

(Think “Microfat micromanagin”)

Question 18

Describe oligodendroglia & schewann cells

Answer 18

• Myelin prevents adjacent neurons from short-circuiting which speeds up the transmission of information as opposed to unmyelinated neurons
• Motor neurons & sensory neurons are heavily myelinated

Oligodendroglia–>(Think “Olive branch separated my friends”)

• Myelinate axons in the brain & spinal cord–> send out large, flat branches that separate adjacent axons
• They have few branches compared to astrocytes

Schwan cells–> (Think “chicken nuggets on a necklace right around the corner”)
-Myelinate axons in the PNS–> wrapping around an axon & forming a structure similar to beads on a string

• Both Oligo & Schwan contribute to nutrition & functioning of neurons–> absorbing chemicals that neuron releases & releases chemicals that neurons absorb
• Damage to Oligo & Schwan is consequential

Question 19

What is the role of glial cells in neuron repair & disease?

Answer 19

• Multiple sclerosis (MS)
• Degenerative NS disorder & common autoimmune disease
• Damage to Oligo that leaves a scar “Sclerosis means scar on neurons in NS pathways
• Leads to impaired information flow–> impaired movement & cognitive function

Question 20

What happens when an axon is cut?

Answer 20

• The severing of motor neuron axons–> unable to move that part
• The severing of sensory neuron axons–> loss of sensation in that part
• Microglia & Schwann cells repair damage to PNS–> paralyzed person may recover after weeks/months
• When PNS axon is cut it degenerates back to cell body
• Microglia remove the debris left by dying axon
• Schwan cells first shrink, then divide–> form glial cells along the axons former path
• The cell body sends out axon sprouts, one of which finds the path formed by Schwann cells and becomes a new axon
• Schwann cells are like signposts guiding axons to their appropriate points
• Schwann cells form new myelin by enveloping new axon

Question 21

Why does damage to the CNS not lead to regrowth/repair (e.g spinal cord cut)

Answer 21

• Because they are too individualized & develop strategies to prevent the regrowth of existing cells
• Oligo cells actually protect the existing structure of CNS by preventing neuron regrowth

Question 22

What factor determines the characteristics & functions of a cell?

Answer 22

• Cell’s proteins do as each cell manufactures thousands of them & they take part in building the cell & communicating with others
• Proteins are involved in memory formation, neuronal malfunctions & restoring function after brain injury
• Water, salt & ions also play a prominent part in cell function

Question 23

Describe the “Cell as a factory” analogy:

Answer 23

• Work centers of a factory cooperate to make & ship proteins
• Just like “factory walls” providing security, the cell’s double-layered outer wall (membrane) separates it from its surroundings & allows for the regulation of what enters & leaves
• The cell membrane is impermeable & contributes to the formation of the cell’s structure & forms a boundary around it.
• Some cell-made proteins are embedded in the membrane where they facilitate the transport of substances in/out of the cell; like “factory gates”
• The cell membrane ensures that the concentration of substances in/out of cells are different
• The cell has an intracellular fluid, while neurons & glia are separated by extracellular fluid made of water & dissolved salts & chemicals
• Organelle membranes function like “workspace dividends” & surround the organelles of the cell–> concentrates needed chemicals while keeping unneeded ones out
• There is a nuclear membrane surrounding the cell’s nucleus “executive office” in which genetic blueprints of proteins are stored, copied & sent to–> endoplasmic reticulum (ER)
• ER is the “factory floor”, an extension of the nuclear membrane where the protein products are assembled in accordance with nucleus instructions
• After assembly, proteins are sent throughout the cell
• Golgi bodies are “Mailrooms” where proteins are packaged for transport
• Microfilaments–> “Cardboard box” reinforce cell structure & aid in its movement
• Microtubules–> “CanadaPost” form transportation network that carries protein into the destination
• Mitochondria–>”Batteries” Cell’s power plants supplying its energy needs
• Lysosomes–> “Deliverymen & garbagemen” vesicles that transport incoming nutrients & remove/store waste
• More lysosome in old cells–> have trouble disposing of their garbage

Question 24

Describe the barrier & gatekeeper function of the cell

Answer 24

• The cell membrane is a phospholipid bilayer that separates extracellular fluid (outside the cell) from the intracellular fluid (inside the cell)
• Also regulates salt & chemical concentrations since lack of balance leads to abnormal functioning
• Phospholipids are molecules that allow the cell membrane regulation
• The hydrophilic head–> contains phosphorus & has polar regions (positive & negative)
• The hydrophobic tails–> consist of hydrogen & carbon atoms tightly bonded to one another by shared electrons. have no polar regions.
• The phosphate groups will bind to water while fatty acid tails have no binding site to water
• The tails point toward each other to avoid the water, while the heads align with one another & point outward to the intra & extracellular fluid
• The bilayer cell membrane is impenetrable to polar water molecules & ions as they carry charges
• Only O2, CO2 & glucose can traverse the bilayer.

Question 25

Describe the role of the nucleus in protein synthesis

Answer 25

• The blueprints inside the nucleus are genes (DNA segments that encode the synthesis of particular proteins)
• Genes are contained within the chromosomes (double helix holding organism’s DNA library)
• Like “Books of blueprints” chromosomes contain thousands of genes for making a protein
• Chromosomes constantly change shape, moving in relation to one another to get the best position in the nucleus (Think of “Ambitious librarians in the office”)
• The gene begins making a protein when chromosomes expose the genes to the surrounding fluid after changing shape
• We have 23 pairs of chromosomes for a total of 46
• Reproductive cells have a total of 23 single chromosomes
• Each chromosome strand has a variable sequence of 4 nucleotide bases that constitute its genetic code: (Thymine, Adenine, Guanine, Cytosine) TAGC
• A on one strand pairs with T, G pairs with C
• The attraction between the bases of each strand of DNA holds it together
• The sequence of TAGC base pairs spell out which amino acid should be assembled to construct a certain protein
• Through the process of transcription (copy part of the message you receive in a text)–>
• Gene segments of the DNA strand unwind to expose their nucleotide bases which serve as a template to attract nucleotides–> form a complementary strand of ribonucleic acid (RNA)
• RNA detaches from DNA & leaves the cell while carrying the code for protein synthesis
• When RNA is produced through transcription–>forms a chain of bases like the DNA (Except that Uracil takes the place of Thymine & is attracted to Adenine)
• The transcribed strand of RNA–> mRNA (messenger)–> carries protein code out of the nucleus to the ER where proteins are manufactured.
• ER is studded with ribosomes which act as catalysts to facilitate protein building. mRNA passes through a ribosome & has its genetic code read (translation)
• The sequence of nucleotide bases in mRNA is transformed into a sequence of amino acids.
• tRNA (transfer) helps translate nucleotide bases into amino acids
• The 3 consecutive nucleotide bases (codons) along an mRNA encode one amino acid. The sequence of codons determines the sequence of the resulting amino acid chain (e.g U, G, G encode tryptophan Trp; UUU encode phenylalanine Phe)
• Humans use 20 amnio acids that are structurally similar, consisting of central carbon atom (C) bound to hydrogen atom (H) & amino group (NH3+), carboxyl group (COO-) and a side chain (R) varying in chemical composition

(Thin “Cute Happy & Not Happy 3 year old, Come Out Of Room”)

• Amino acid chains are also called polypeptide chains because each NH3+ group is bound to the COO- group of the adjacent amino acid by a peptide bond.
• Polypeptide chains can be made from 20 amino acids (20 x 20)= 400 for dipeptides, (20 x 20 x 20)= 8000 for tripeptides.

Question 26

What is the simple process of building a protein?

Answer 26

DNA–> mRNA–> Protein

Question 27

What are the 4 levels of a protein structure?

Answer 27

• Long polypeptides–> twist into helices (spirals)–> pleated sheets–> fold together & form complex shapes
• In rare circumstances, misfolded proteins wreak havoc (common with prion proteins implicated in mad cow disease, Alzheimer & Parkinson)

Question 28

How many proteins & how many genes can a neuron contain?

Answer 28

-1 neuron contains 20000 genes–> genes can produce 20000 protein molecules (number of proteins produced always larger than the number of genes)

Question 29

Name some of the abilities of proteins:

Answer 29

1) Can be cleaved into pieces by enzymes & combine with other proteins to form newer ones
2) Can modify length, shape, behaviour of other proteins & act as enzymes (enhance chemical reactions)
3) Can regulate substance flow across the cell membrane
4) Can be exported to another cell & act as messenger molecules

Question 30

What is the role of Golgi bodies?

Answer 30

• Protein molecules that have been synthesized are wrapped in membranes & marked with postal addresses
• Wrapping & labelling is the responsibility of Golgi bodies
• Getting proteins to the right destination (like CanadaPost)
• Then proteins are loaded into motor molecules that carry each protein to its destination, travelling through microtubules

Question 31

What are the 3 possible locations for proteins to be transferred to?

Answer 31

-If the protein is destined to:
A) stay in the cell–> unloaded in intracellular fluid
B) Incorporated into cell membrane–> carried to the membrane & inserted
-Responsible for the transport of small molecules (i.e salts, sugars etc. across the membrane)
C) Exported from the cell–> exocytosis “out of the cell” transferred out

Question 32

What are 3 reasons for a protein to change shape?

Answer 32

-Protein’s shape determines its function
-It is dependent on the amino acid sequence that composes its molecule; analogous to a lock in a door
-The surface of proteins have a groove (receptor); analogous to a keyhole
May change shape:
- After binding with other chemicals
- As a function of temperature
- As a response to changes in electrical charge

Question 33

What is the channel, gate, pump analogy on proteins embedded in the cell membrane?

Answer 33

• Some membrane proteins form diff sized channels through which diff sized substances can pass
• Protein channels may allow potassium, sodium, chloride to pass in & out among other substances
• A gated channel changes shape to allow passage when open & to prevent passage when closed
• Protein may change shape to act as a pump & carry substances across the membrane

Question 34

Describe the difference between autosomes & sex chromosomes:

Answer 34

• Genotypes (genetic makeup) influence phenotypes (physical & behavioural characteristics)
• Human genome project cataloged 20000 genes
• James Watson noted that Neandertals have a similar genome to humans
• Gregor Mendel studied how genes influence our traits
• One member of each pair of chromosomes come from mother & one from father
• Chromosome 1 is the largest.
• The 23rd pair are X & Y sex chromosomes (determine sexual characteristics) while pairs 1-22 are autosomes (determine appearance & behaviour)
• Females have XX, males have XY
• Y chromosome contains SRY protein (Sex determining region)–> triggers testes development–> male phenotype
• Each cell contains 2 copies of every gene (alleles) since sex chromosomes are matched pairs
• The nucleotide sequence in a pair of alleles may be identical or different (homozygous vs heterozygous)

-Common nucleotide sequence in a population–> wild-type allele which may have a less common sequence–> mutation (neutral, beneficial or harmful)

Question 35

What are dominant vs recessive alleles?

Answer 35

Homozygous alleles–> encode the same protein
Heterozygous alleles–> encode somewhat different proteins
3 out of heterozygous condition:
1) Only 1 allele from mother expressed
2) Only 1 allele from father expressed
3) Both alleles expressed simultaneously

-Therefore, the dominant allele is a member of the gene pair that is routinely expressed as a trait, whereas the one that is not expressed is the recessive allele

• If allele’s trait is expressed in phenotype (in complete dominance)
• If it is only partially expressed (in incomplete dominance)
• If expressed along with trait of the other allele in the gene pair (in codominance)

Question 36

Describe genetic mutations:

Answer 36

• When errors occur in the nucleotide sequence when reproductive cells make gene copies–> alleles get altered leading to mutations
• Polymorphism (SNP)–> a single nucleotide base change
• Results in codon change–> change in one amino acid in a protein–> alters the protein’s function
• There are more than 1000 ways in which to have a predisposition to or increased resistance to cancer just from the BRCA1 breast cancer gene found on chromosome 17

Question 37

What is sickle-cell anemia?

Answer 37

• An SNP in which a T base is substituted for an A base in the hemoglobin gene on chromosome 11
• Blood cells take on an abnormal sickle shape
• Leading to poor oxygen capacity, weakening the person & offering resistance to malaria
• It is the most common genetic blood disease

Question 38

What are acquired genetic mutations?

Answer 38

• Non-inheritable mutations that can affect the behaviour of the carrier
• Mitotic mutations–> due to cell division errors occurring during development
• Errors in each neuron accumulate at the rate of one per week
• By 80 years of age, a neuron may have up to 2000 mutations likely to have negative effects

Question 39

Name an allele disorder that affects the brain:

Answer 39

Tay-Sachs disease named after its founders
-Caused by dysfunction in the gene that produces HexA on chromosome 15
-Responsible for breaking down a class of lipids in brain cells–> dysfunction leads to accumulation of lipids–> cell damage
-Symptoms appear a few months after birth
-Seizures, bad eyesight, low motor & mental abilities–> dead within a few years
-European Jews & French Canadians most susceptible
-Can only inherit this disease when both parents pass on the recessive allele
- Parents must possess a corresponding dominant wild-type HexA allele for that gene pair since they have survived to adulthood
-Their egg & sperm contain a copy of the wild-type or the mutation & which one gets passed on is completely by chance
A) The child either has 2 wild types–> no disorder, no passing on
B) The child has 1 wild-type, 1 mutation–> no disorder, carrier
C) The child has 2 mutations–> disorder, passing on

Question 40

Describe the inheritance patterns of a mutation:

Answer 40

A) Recessive condition:
If both parents are carriers:
-25% chance for offspring to get the disease
B) Dominant condition:
If a person with the disease mates with a non-carrier:
-50% chance for offspring to get the disease
If both people have the disease
-75% chance for offspring to get the disease

If one parent is a carrier & the other is normal, the child has a 50% chance of becoming a carrier but no chance of having the disease

-A blood test can determine if this is the case

Question 41

Describe Huntington disease:

Answer 41

• The buildup of an abnormal version of huntingtin (HTT) protein that kills brain cells in basal ganglia & the cortex
• Symptoms often start in midlife & include abnormal involuntary movements, memory loss & death
• Used to be called chorea (Greek for “dance”)
• For Tay-Sachs 2 copies are required to exhibit the trait because it is recessive
• For HTT only 1 copy is required because HTT is a dominant allele
• If one parent has the mutation–> 50% chance of having the disorder
• If both parents have the mutation–>75% of having the disorder

Question 42

Describe chromosome abnormalities:

Answer 42

Copy number variations–> autism, schizophrenia, learning disabilities

Down syndrome is caused by extra chromosome 21 (smallest chromosome) copy which is usually passed down by the mother, yielding 3 chromosomes–> trisomy which affects the phenotype
-Short stature, distinct facial features, heart defects, respiratory infections, intellectual impairment, prone to leukemia & Alzheimers, short life span

Oftentimes this variation is beneficial or has little consequence
-E.g people who have 15 copies of the AMY 1 (amylase) gene instead of 6 copies can digest starchy food better

Question 43

Describe different methods of genetic engineering

Answer 43

-Manipulating a genome (removing/adding/modifying)
Selective breeding:
-Oldest means of influencing genetic traits
-Dog brain became smaller than a wolf’s brain with more cortical neurons which accounts for its sociability

Cloning

• Altering early embryonic development by producing an offspring that is genetically identical to another animal
• Cell nucleus containing DNA is placed in an egg with a removed nucleus–> stimulate division & implant new embryo in the uterus of a female
• Example of Dolly the sheep, Scamper the horse & Copycat the cat & Asian gaur the cow.

Transgenic techniques:
-Introduce genes into an embryo or remove genes from it
Knock-in–> gene is added to the genome of another species, passed along & expressed in the subsequent generation
-Inactivate a gene so that a line of lab animals fail to express it–> examine whether an absent gene is responsible for a specific function/disorder
Knockout–> introduce a gene for human ADHD in a line of rats to explore methods of treatment

Genetic modification

• Altering genetic code through CRISPR
• The molecular mechanism involved in identifying an invading virus by its unique DNA sequence–> modified in the lab to produce an RNA sequence that can identify specific parts of the DNA in any gene
• Using the CRISPR method, the gene can be cut, a portion of it deleted & replaced by another DNA squence–> gene editing
• Used to identify cancer cells, make animal models etc.

Question 44

Describe phenotypic plasticity:

Answer 44

Individuals have the capacity to develop into more than one phenotype

• Due to the genome’s capacity to express a large number of phenotypes
• Due to the influence of environment & experience in phenotypic expression

Question 45

What is concordance?

Answer 45

Incidence of similar behavioural traits between identical twins for vast array of diseases is between 30-60%

• For cleft palate & breast cancer–> 10% concordance rate
• The less than perfect concordance rate is due to epigenetic factors

Question 46

What is the role of epigenetics in gene expression?

Answer 46

• -Describing epigenetic code is the work of IHEC
• Cell’s environment determines what kind of tissue & NS gets developed
• Epigenetic mechanisms–> Cause phenotypic variations without any alterations in the base pair nucleotide sequence of genes
• The epigenetic mechanism can influence protein production by blocking a gene–> prevent transcription or by unlocking a gene–> induce transcription

Question 47

What are some steps to stop gene transcription?

Answer 47

Steps to stop transcription:

1) DNA must be unpooled from its wrapping (histone) & it can be stopped from unwrapping.
2) A methyl group (CH3) bind to the tails of histones, either blocking them from opening or allowing them to open
3) The methyl group (M) bind to CG base pairs to block transcription
4) Non-encoding RNA (ncRNA) binds to mRNA, preventing translation

Question 48

Can nutritional experiences affect offspring health?

Answer 48

Bygren & colleagues studied famine in the Swedish region

• Propose that diet during a critical period can modify the genetic expression of sex chromosomes & pass it on to subsequent generations
• Highlighting the importance of diet in the prepubertal period when gene expression in sex chromosome begins