hbio_exam_20241019053917 Flashcards
sCell Body Function
Contains Nucleus and is Responsibile for controlling the functioning of the cell
Dendrite Function
Carries messages/nerve impulses towards cell body
Axon Function
Carries messages/nerve impulses away from the cell body
Schwann cells vs Oligodendrocytes
Oligoden— produce myelin sheath inside the CNS whilst Schwann cells produce myelin sheath outside the CNS
3 Functions of Myelin Sheath
Act as an insulator
Protects axons from damage
Speeds up movement of nerve impulses along the axon
Nodes of Ranvier
Gaps at intervals along the axons in the myelin sheath
Neurilemma
Outermost coil of the Schwann cell forms a structure around myelin sheath - helps repair injured fibres
Neuron
A nerve cell
Nerve Fibres
Any long extension of the cytoplasm of a nerve cell body - very long axons
Nerve
Bundles of nerve fibres held together by a connective tissue
Interneurons Function + 3 examples
To link sensory and motor neurons
Association neurons
Connector neurons
Relay neurons
Electrochemical change meaning
- A change in electrical voltage
- Brought about by changes in chemicals: concentration of ions inside/outside cell membrane of neuron
Potential difference meaning
The potential for a group of positive + negative charges to come together and release energy
Membrane potential meaning
Difference between ion concentration means there is a potential between inside and outside of cell membrane
How do ions diffuse through CM
Use channel proteins such as leakage and voltage-gated channels to diffuse through phospholipid bilayer
Leakage vs Voltage-gate channel proteins
Leakage is open all the time
Voltage-gate is only open when nerve is stimulated
What ions does intracellular fluid contain a high concentration of
K+ and organic substances made by cell
What ions does extracellular fluid contain a high concentration of
Na+ and Cl- ions from NaCl
Sodium Potassium Pump
Pump moves 2K+ into cell for every 3Na+ removed from cell; net reduction of positive ions in cell
Must use ATP to move against concentration gradient - active transport
Polarised Membrane meaning
Because of a net outflow of positive ions out of the cell through the sodium potassium pump and in addition to negative organic ions inside cell result in inside of cell being more negative
Produces a negative resting membrane potential thus, membrane is said to be polarised
Occurance of Action Potential (3 marks)
Occurs due to the opening + closing of voltage-gated channels which causes a rapid depolarisation + repolarisation of membrane
How does a nerve impulse occur
A single action potential occurs in one section of a membrane
This then triggers an action potential in the adjacent membranes - continues along the length of a neuron, known as a nerve impulse
Conduction/Transmission along unmyelinated fibres
Depolarisation of one area of the membrane causes a movement of Na+ into adjacent areas
This stimulates the opening of voltage-gated sodium channel in the next part of the membrane
Then initiates action potential in that area of the membrane and the process repeats itself along the whole length of the membrane - action potential moves along the membranre away from stimulation point
Why can’t nerve impulses travel backwards
Impulses travel in both directions along the fibre, away from stimulation point but nerve impulses cannot go backwards due to refractory period - another action potential cannot be generated at that point on the fibre
Why cant action potential occur on myelinated fibres
Ions cannot flow between inside + outside of membrane due to the nerve fibre being surrounded by myelin
Transmission along myelinated fibres
Saltatory conduction - Action potential jumps from one node of Ranvier to the next, allowing nerve impulses to travel much faster along myelinated fibres then unmyelinated fibres
Why do weak stimulus + strong stimulus produce same action potential
All-or-nothing response - size of nerve impulse is not related to the strength of the stimulus
2 reasons of a stimuli being distinguished through different intensities
Strong stimulus causes depolarisation of more nerve fibres than weak stimulus
Strong stimulus produces more nerve impulses in a given time than weak stimulus
What is a synapse
A small gap between adjacent neurons
How are neurotransmitters removed from the synpase
They are reabsorbed by presynaptic membrane and degraded by enzymes or moving away through diffusion
3 types of neurotransmitters
Acetylcholine, Adrenaline, Dopamine, Histamine, Noradrenaline
2 Ways in which nerve impulse across a synpase occurs
Axon -> Dendrite
Axon -> Cell body
Chemicals which stimulate transmission at synapse/neuromuscular
Caffine, Benzedrine
Chemicals which depress transmission at synpase/neuromuscular
Anesthetics, Hypnotics, Venom from animals
How do nerve agents lead to death
Contain organophosphates, which cause a build-up of acetylcholine at neuromuscular junction
As a result, all muscles in body try to contract which leads to a loss of muscle control preventing breathing and leading to death
What is a nueromuscular junction
Gap vetween motor nerve cell + muscle fibre
3 ways in which pain receptors are stimulated
Damage to tissues - cut or heavy bump
Poor blood flow to tissue
Excessive stimulation from stimuli - chemicals, heat
Reflex definition
A rapid, automatic response to a change in external/internal enviro
4 main properties of a reflex
Reflex is triggered by a stimulus - not spontaneous
Reflex is involuntary - without consious thought
Reflex is rapid - only a small number of neurons are involved
Reflex response is stereotyped - occurs in same way each time
Where are most reflexes coordinated and how
Spinal cord
- impulses from receptors can be pased to motor nuerons at same level in spinal cord
- impulses from receptors can travel up a few segments up or down spinal cord before travelling out through motor neuron
5 main components of a Reflex
- Receptor - reacts to a change in the internal/external environment by initiating a nerve impulse in the sensory neuron
- Sensory neuron - carries impulses from the receptor to the spinal cord or brain
- Synapse - nerve impulse may be passed directly to a motor neuron, or there may be one or more interneurons that direct the impulse to the correct motor neuron
- Motor neuron - carries the nerve impulse to an effector
- Effector - receives the nerve impulse and carries out the appropriate response
- Effectors are muscle cells or secretory cells
2 examples of reflexes in body
Saliva is response to sight, smell, taste of food
Ejaculation of semen
Moving limbs from painful stimulus
Innate reflexes vs Acquired reflexes
Innate reflexes consist of suckling, chewing or following movements with eyes - present at birth
Acquired reflexes are more complex motor patterns such as riding a bike, jamming on breaks, catching a ball - learnt through constant repetition
What is CNS made up of
brain + spinal cord
3 Structures protecting CNS
Bone (Cranium + Vertebrae)
Mebranes - known as meninges
Cerebrospinal fluid
What are meninges membranes made up of (1 mark)
Connective tissue
3 types of meninges
Dura Mater - outer meningeal layer, tough + fibrous
Arachnoid Mater - middle meningeal layer, loose mesh of fibres
Pia Mater - Inner layer, contains many blood vessels sticking closely to CNS surface
Where is CSF found
Occupies a space between middle + inner layers of meninges OR central canal in spinal cord
What is CSF made up of
Clear watery fluid containing a few cells, some glucose, protein, urea + salts
3 Functions of CSF
- Protection: acts as a shock absorber, cushioning any blows or shocks CNS may sustain
- Support: the brain is suspended inside the cranium and floats in the fluid that surrounds it
- Transport: CSF is formed by blood and circulates around the CNS before re-entering blood capillaries; During its circulation, it takes nutrients to the cells of the brain and spinal cord and carries away their wastes
Corpus Callosum Structure + Function
- Wide band of nerve fibres that lies underneath the cerebrum at the base of the longitudinal fissure
- Nerves fibres in the corpus callosum cross from one cerebral hemisphere to the other and allows the two sides of the cerebrum to communicate with each other
Cerebellum Surface Structure
- Surface is folded into a series of parallel ridges
- Outer folded part of the cerebellum is grey matter
- Inside is white matter that branches to all parts of the cerebellum (like tree branches)
Cerebellum Function
- Cerebellum exercises control over posture, balance and coordination of voluntary muscle movement - receives sensory info from the:
- Inner ear for info about posture and balance
- Stretch receptors in the skeletal muscles for info about the length of muscles
Helps with smooth, coordinated movements
What happens of cerebellum is damaged
Impulses don’t originate in the cerebellum, so we could still move but movements would spasmodic, jerky and uncontrolled
5 Functions of Hypothalamus
- Body temperature
- Food + water intake
- Patterns of waking and sleeping
- Contraction of the urinary bladder
- Emotional responses - fear, anger, pleasure
- Autonomic nervous system - heart rate regulation, blood pressure, secretion of digestive juices, alimentary canal movements, pupil diameter
- Secretion of hormones and coordination of parts of the endocrine system - regulates metabolism, growth, reproduction and responses to stress through pituitary gland
Medulla Oblongata 3 Centres + Function
- Cardiac centre - which regulates the rate and force of the heartbeat
- Respiratory centres - which control rate and depth of breathing
- Vasomotor centre - regulates the diameter of blood vessels
- Other centres regulate reflexes of swallowing, sneezing, coughing and vomiting
- Also serves as a passage of nerve fibres passing through the medulla going to other parts of the brain
2 Main Functions of Spinal Cord
- Carry sensory impulses up to the brain and motor impulses down from the brain
- To integrate certain fast, automatic responses - reflexes
How is spinal cord allowed to bend
Space containing fat, connective tissue and blood vessels serves as padding around spinal cord
What is grey matter composed of
nerve cell bodies + unmyelinated fibres
How are myelinated nerve fibres arranged in spinal cord
arranged in bundles known as ascending/descending tracts
Ascending Tract vs Descending tracts
- Ascending tracts - sensory axons that carry impulses upwards, toward brain
- Descending tracts contain motor axons that conduct impulses downwards, away from the brain
Where is grey matter found in spinal cord
Grey matter is at the centre of the spinal cord, surrounded by white matter
Where is grey matter found in brain
Can be found deep in the cerebrum or on outer surface surrounding white matter
What does grey matter consist of in brain
neuron cell bodies, dendrites and unmyelinated axons
Purpose of grey matter in brain
sevres to process info
What is basal ganglia and what is its function
Grey matter found deep in cerebrum - consists of groups of nerve cell bodies associated with the control of skeletal muscles
Function concernes initiating desired movements and inhibiting unwanted movement
2 Functions of white matter in brain
- Allows communication to and from grey matters areas
- Allows communication between grey matter and other parts of the body
Convolutions/gyri
Folding of cerebral cortex producing rounded ridges
Sulci/Sulcus vs Fissures
Sucli - Shallow downfolds between convolutions of the cerebral cortex
Fissures - deep downfolds between convolution of the cerebral cortex
5 Lobes of cerbral hemisphere
Insula
Frontal
Temporal
Occipital
Parietal
Function of frontal lobe
Thinking, problem solving, emotions, personality, language, and control of movement
Parietal lobe
Processing temperature, touch, taste, pain and movement
Temporal lobe
Processing memories and linking them with senses; receives auditory info
Occipital lobe
Vision
Insula
Recognition of different senses and emotions, addiction and psychiatric disorders
3 Main Functional areas of cerebral cortex
- Sensory Areas - receive and process nerve impulses from the senses
- Motor Areas - send impulses to muscles, especially for voluntary movement
- Association Areas - concerned with intellectual + emotional processes
How are memories stored
Exist as a pathway of nerve cells - new links are made between neurons or existing links are modified
Specialised functions in left vs right hemisphere
- Language ability is normally controlled by the left hemisphere
- Musical and Artistic abilities are controlled by the right hemisphere
Tracts vs Nerves
Within CNS, bundles of nerve fibres are called tracts; outside the CNS they are called nerves
3 Types of Tracts occuring in white matter
- Tracts that connect various areas of the cortex within the same hemisphere
- Tracts that carry impulses between left and right hemispheres
- Tracts connecting the cerebral cortex to other parts of the brain or to the spinal cord
Function of Peripheral Nervous System (PNS)
Peripheral Nervous System (PNS) takes messages from receptors to the CNS and from the CNS to muscles and glands
2 things PNS is composed of
- Nerve fibres that carry info to and from the CNS
- Groups of nerve cell bodies - ganglia, which lies outside the brain and spinal cord
Cranial Nerves Structure (4 marks)
- 12 pairs of nerves arising from the brain - such as auditory and optic nerve
- Most cranial nerves are mixed nerves - contain fibres carrying impulses to the brain and away from the brain
- Fibres that carry impulses into the CNS are called sensory fibres
- Fibres that carry impulses away from the CNS are called motor fibres
Spinal Nerves Structure (4 marks)
- 31 pairs of nerves arising from the spinal cord
- These are all mixed nerves - contain both sensory + motor fibres
- Each nerve is joined to the spinal cord by two roots
- Ventral root contains the axons of motor neurons - have their cell bodies in the grey matter of the spinal cord
- Dorsal root contains the axons of sensory neurons - have their cell bodies in a small swelling on the dorsal root - known as dorsal root ganglion
Divsions of the Afferent division
- Somatic sensory neurons - brings impulses from the skin and muscles
- Visceral sensory neurons - brings impulses from the internal organs
Afferent division definition
Afferent (sensory) division of PNS has fibres that carry impulses into the CNS by sensory neurons from receptors in the skin and around the muscles and joints
Efferent Division definitions
Efferent (motor) division has fibres that carry impulses away from the CNS
Divisions of Efferent Division
- Somatic division (somatic nervous system), takes impulses from the CNS to the skeletal muscles
- Autonomic division (autonomic nervous system), carries impulses from the CNS to heart muscles and other involuntary muscles + glands - can be divided into
ANS definition + operation + 3 Functions
- (ANS) controls the body internal environment - involved in many mechanisms that keep it constant
- Operates without conscious control and is regulated by groups of nerve cells in the medulla oblongata, hypothalamus and cerebral cortex
- Functions of the Autonomic Nervous System include:
- Heart Rate
- Blood Pressure
- Body Temperature
- Digestion
- Release of energy
- Pupil diameter
- Air flow to the lungs
- Defecation
- Urination
Pathway of ANS
- Carry impulses to the heart muscle, other muscles of the internal organs and the glands
- Impulse travels along two neurons from the CNS to an organ controlled by the ANS
- First neuron is myelinated and has its cell body in the CNS
- Second neuron is unmyelinated and has its cell body in a ganglion - group of nerve cell bodies outside the CNS
- Impulse travels along two neurons from the CNS to an organ controlled by the ANS
4 Differences between autonomic and somatic
Autonomic Division has effectors of heart muscle and other involuntary muscles + glands, Somatic concerns skeletal (voluntary) muscles
Autonomic division function is for an adjustment of internal enviro (homeostatis) while Somatic Division is responses to external environment
Control of ANS is usually involuntary whilst SNS is usually voluntary
ANS effect on target organ is either excitation or inhibition but SNS is always excitation
ANS consists of 2 sets of nerve to target organ (sympathetic or parasympathetic) whilst somatic division is just one set of nerves
Parasympathetic vs Sympathetic + Nerve endings for each
- Parasympathetic division generally produces responses that maintain the body during relatively quiet conditions
- Parasympathetic nerve endings release acetylcholine
- Sympathetic division tends to produce responses that prepare the body for strenuous physical activity - known as fight-or-flight response (prepares body for situations that may involve aggression or fleeing from a threat)
- Sympathetic nerve endings release noradrenaline
Sympa vs Parasympa effects on body (4)
Sympa dilates pupils, increases sweat secretion, decreases saliva secretion, constricts skin blood vessels, Relaxes urinary bladder walls, Dilates Bronchioles of lungs
Immune response definition
Defined as a response triggered by foreign substances or micro-organisms entering the body causing lymphocytes such as B + T-cells to respond
Where a B-cells + T-cells produced and how do they mature
- Half the cells produced by bone marrow go to thymus to mature into T-Cells - become a part of lymphoid tissue
- Other half stays in bone marrow and mature into B-cells - become a part of lymphoid tissue
2 parts of an immune response
- Humoral Response; Antibody-mediated immunity - involves the production of antibodies by B-cells - circulate around the body and attack invading agents
- Cell-Mediated Response - Occurs due to T-cells - involves the formation of special lymphocytes that destroy invading agents
Antigen definition and examples
Described as any substance capable of causing a specific immune response
proteins, carbohydrates, lipids, nucleic acids, Virus particles, Micro-organisms, Toxins, Egg whites
Self Antigen vs Non-self antigens
- Self Antigens - any large molecule produced in a person’s own body; does not cause an immune response in that person
- Non-self antigens - any foreign compound to the body that triggers an immune response
- Immune system only attack non-self antigens; prescribed at birth
Antibodies definition
Defined as a Y-shaped specialised proteins produced by plasma cells in a response to a non-self antigen
What are plasma cells
Plasma cells are cells that develop from a B-cell and produce antibodies
Ways in which antibodies work
- Inactivate foreign enzymes or toxins by combining with them or inhibiting their reaction with other cells/compounds
- Bind to the surface of viruses and prevent them entering cells
- Coat bacteria so its more easily consumed by phagocytes
- Cause agglutination - particles such as bacteria, viruses and foreign blood cells to clump together
- Dissolve organisms
- React with soluble substances to make them insoluble and thus, more easily consumed by phagocytes
Primary Response vs Secondary response (7 marks)
-
Primary response - Immune reaction to a first exposure to an antigen
- Immune response is fairly slow - takes several days to build up antibodies
- Takes time for B-cells to multiply and differentiate into plasma cells and then secrete antibodies
-
Secondary response - Immune reaction to a secondary or subsequent exposure to an antigen
- Much faster as memory cells recognise antigen much quicker
- Thus, plasma cells can form very quickly and antibody levels in blood plasma rise to a higher level and lasts longer
- Consequently, antigen has little opportunity to exert any real effect of body - no illness result
- Much faster as memory cells recognise antigen much quicker
Immunisation definition
Immunisation refers to programming the immune system so that the body can respond to infecting micro-organisms
Vaccination definition
Vaccination is the artificial introduction of antigens of pathogenic organisms so that the ability to produce appropriate antibodies is acquired without the person having to suffer the disease
4 main types of vaccines + example for each
-
Live attenuated vaccines: micro-organisms with a reduced ability to produce disease symptoms (reduced virulence)
- Immunised person doesn’t contract disease but manufactures antibodies against the antigen
- Examples include polio, Tuberculosis, rubella, measles
-
Inactivated vaccines: contain dead micro organisms which produce a shorter lasting immunity
- Examples Cholera, Typhoid, Whooping cough
-
Toxoid Vaccines: where bacteria produce their effects in humans by liberating toxins
- Toxins produced by bacteria can be inactivated so they do not cause actual illness in individual (known as toxoids)
- Examples include diphtheria, tetanus
-
Sub-unit Vaccine: A fragment of the organism can be used to provoke the immune response
- Examples include Human Papilloma Virus (HPV, Gardasil) and Hepatitis B
Why cant vaccinations occur too soon after birth
- This is because the child’s blood contains antibodies from its mother via placenta or breast milk
- If a newborn is vaccinated, antibodies from the mother would eliminate the antigens in the vaccine
- Occurs before the child’s immune system can create an immune response
Why is one injection of a vaccine not usually enough
- One injection of vaccine is not usually enough
- The antibody level from primary response following the first vaccination will decline - a second vaccination (booster) is needed to stimulate a secondary response
- The memory cells react quickly to this second exposure - results in a higher, longer-lasting level of antibodies in addition to more memory cells`
- The antibody level from primary response following the first vaccination will decline - a second vaccination (booster) is needed to stimulate a secondary response
Why does there need to be a gap between OG shot and booster shot? What is the usal gap length
If booster is too soon after first jab, antibodies present in blood will eliminate the material of vaccine before more B-cells can be activated
2 Month gap
Herd Immunity
Herd immunity - a group immunity that occurs when such a high proportion of people in a population are immunised that those who are not immune are protected: less chance of disease being transmitted through a population
Bactericidal vs Bacteriostatic Antibiotics
- Bactericidal antibiotics - kill bacteria by changing the structure of the cell wall or membrane and disrupting the action of essential enzymes
- Bacteriostatic antibiotics - stop bacteria from reproducing, usually by disrupting protein synthesis
Multiple vs Total drug resistance
- Multiple drug resistance - resistance of some strains of bacteria to most of the available antibiotics
- Total drug resistance - resistance of some strains of bacteria to all antibiotics
What are receptors
structures that is able to detect a change in the body’s internal or external environments
What are antibiotics
defined as chemical able to inhibit the growth of, or kill micro-organisms, particularly bacteria
Why is it difficult to treat viruses
- Viruses enter host cells, and virus DNA or RNA induces the cell to produce new virus particles which leave the cell to infect new hosts
- This makes it difficult to treat as any drug that interferes with virus replication will likely be toxic to the host - leads to cell damage
3 overall Factors which can affect if individuals want to be vaccinated
Inability to be vaccinated due to health issues
Social Factors
Cultural Factors
Economic Factors
Explain 2 factors concerning an inability to be vaccinated through health issues
-
Allergic Reactions: may occur from the vaccine or a reaction to the medium in which the vaccine was cultured - reaction to vaccine components
- Many influenza vaccines are manufactured in fertilised eggs - Allergy to egg protein may have a reaction
- Preservatives: Preservatives used in vaccine can apparently affect the nervous system and lead to other health issues
Explain 4 factors concerning social factors against vaccines
- Ethical concerns with animal use: Manufacture of viral vaccines requires host tissue as viruses can only reproduce in living cells; people are concerned about treatment of animals in production of vaccines
- Ethical concerns of human tissue use: Many vaccines require human tissue as some viruses don’t grow well in other organism cells and avoids cross-species infection from unknown viruses; concern for many people
-
Ethical concerns with informed consent: Concern that trialling vaccines in developing countries with not a high education standard
- Individual do not fully understand risks and can be exploited by the vaccine manufacturer
- Concerns about sexual activity in teenagers: Vaccinating against sexually transmitted infection HPV will encourage teenagers to be sexually active
- Availability: Vaccine may not be readily available in all areas
Explain Cultural Factors affecting vaccines
-
Religious beliefs - religions relying on faith healing and healing through prayer such as First Church of Christ are opposed to vaccinations
- Some methods used to produce vaccines may also contradict religious beliefs
Explain 2 Economic Factors concerning vaccines
- Cost of vaccine - The vaccines may be too expensive for individuals to afford
- Commercialisation - Interests of commercial vaccine production may affect its use
Gene defintion
A sequence of nucleotides in a DNA molecule that codes for a specific characteristic
Allele definition
An alternative form of a gene
Allele Frequencies
Frequency of occurrence of a certain characteristic in a population
Gene pool
The sum total of all of the alleles available among the interbreeding members of a population of a particular species
Gene-flow
The movement of genes from one population to another or from one part of a population to another as a result of reproduction between individuals from each population
Population
Group of organisms of the same species living together in a particular place at a particular time
Genotype vs Phenotype
- Genotype - the inherited genetic make-up of an individual (BB, bb, Bb)
- Phenotype - the observed expression of the alleles for the characteristic; physical appearance
- Phenotype is determined by the genotype and the environment
Monogenic vs Polygenic Inheritance
- Monogenic Inheritance - exists when an individual receives just one pair of alleles for a trait
- Traits are discrete - either trait is present or is not present
- Example is blood grouping
Polygenic Inheritance - many pairs of genes control the trait
- Continuous variation in the trait - alleles will have an additive effect
- Examples include skin colour, height and weight
- Continuous trait = many phenotypes
3 Assumptions of Polygenic Inheritance
- Each gene has two kinds of alleles, contributing and non-contributing
- There is no dominance
- The effect of each contributing allele is additive
Variation definition
Variation is described as the differences that exist between individuals or populations of a species
5 Mechanisms of Vairation
- Mutations - Only mutations in sex cells can be passes on to offspring
- Random mating/random selection of a partner
- Sexual Reproduction
- Chance meeting of sperm and egg cells during fertilisation
- Environmental factors - diet, difference in weight + muscle size; as a result of epigenetics
How does crossing over contribute to variation
- Crossing over of homologous chromosomes occurs in prophase 1 of meiosis 1
- Exchange of DNA between paired homologous chromosomes of each parent results in new combinations of alleles in the gametes formed, ensuring variation
How does independent assortment contribute to variation
Independent assortment of homologous chromosomes to poles occurs during anaphase 1
- During meiosis, homologous chromosomes are randomly distributed to daughter cells
- Different chromosomes segregate independently of each other resulting in gametes with unique combinations of chromosomes; variation
How does independent alignment of homologous chromosones contribute to variation
Independent alignment of homologous chromosomes on equator occurs during metaphase 1
- During metaphase, each pair of recombined homologous chromosomes line up along the equator of the cell
- Either homologue may orientate towards either pole (end of the cell) randomly and independently, known as Random Orientation
Mutation defintion
a sudden change in the structure or quantity of an organism’s genetic material leading to new characteristics
Gene mutation
a change in one or more nucleotides in a strand of DNA
2 Causes of mutations
Induced + Spontaneous Mutations
Induced mutations
- Induced mutations are caused by mutagens (mutagenic agents)
- These mutagens increase the rate of mutations
- Examples of mutagens include ultraviolet light, X-rays, cosmic rays, radiation from radioactive waste and some antibiotics
- A mutation will cause a mutant
Mutant
an organism with a characteristic resulting from a mutation
Spontaneous Mutations
- A mutation that occurs due to an error in a natural biological process
- For example, errors in mitosis or meiosis
Frameshift Mutations
- A mutation involving an insertion or a deletion that results in a change in the way that the sequence is read
- Results in the series of three bases that code for an amino acids starting at the different base - affects the outcome of the DNA from that point on
Why don’t frameshift mutations occur when 3 bases are added or deleted
- In this case, DNA will simply code for one more, or one less, amino acid, but the rest of the amino acids will be the same
- Would still be a mutations; not frameshift
Aneuploidy
a change in the chromosome number as a result of non-disjunction
- during meiosis, a chromosome pair doesn’t separate and so one daughter cell has an extra chromosome and one daughter cell has one less than normal
Migration definition
The movement of individuals between populations, enabling gene flow
Gene flow
Gene flow is the movement of genetic material from one population to another
Immigration vs Emigration
Immigration
- Introduces new genes to form a gene pool
Emigration
- Causes genes to be lost to other gene pools
Geographical Barriers Definition + Examples
- When a physical barrier prevents two groups of the same species from meeting and interbreeding
- Examples include mountain ranges, deserts, oceans or land clearing
What is meant by adaptive radiation
Environment conditions on either side of the barrier frequently differ - leads to the group on each side of the barrier adapting to its own environment
Sociocultural Barriers + Examples
- Factors such as economic status, educational background and social position are barriers to interbreeding
- People who speak different languages will not breed
- Some religions prohibit marriage outside the religion
Natural Selection
- Natural selection is defined as a process by which a species becomes better adapted to its environment
- Those individuals with favourable characteristics have a survival advantage - pass on characteristics on to subsequent generations
3 Observations for natural selection
Variation
- All members of a species vary
- Variations were passed on from one generation to the next, with characteristics displayed by the parents being passed on to their offspring
Birth Rate
- All living organisms increase their numbers at a far greater rate than their resources - food supply
- Results in overcrowded
Nature’s Balance
- Although birth rate is very high - each species tended to maintain their numbers at a constant rate
- Known as concept struggle for survival - excessive birth rate and limited resources
Process of Natural Selection
- Variation in Phenotype (expression of genotype) must exist in a gene pool
- More offspring are produced than can survive
- An environmental selection pressure, must exist - any factor that threatens the survival of a species
- Examples: Predators, climate, competition
- Selective pressures change the gene frequencies within the population
- A struggle for survival exists - caused by competition for food, space, water, avoiding predators and finding mating partners
- Individuals with favourable characteristics/alleles are naturally selected and will survive at a greater rate than those with unfavourable characteristics
- Survival of the fittest - individuals ability to survive and reproduce
- Individuals with favourable characteristics/alleles are naturally selected and will survive at a greater rate than those with unfavourable characteristics
- Favourable alleles are passed on to the next generation
- In the offspring, the allele frequency of the favourable characteristic will increase in their population
- The same selective pressure must act on the population over many generations in order for the frequency of favourable alleles to increase in the gene pool and population over time
Eskimos Criteria
- Long bodies and short limbs
- Smaller SA to Volume ratio
- Reduces heat loss, conversing heat - favourable in colder climate
Africans Criteria
- Short bodies and Long limbs
- Larger SA to Volume Ratio
- Increase heat loss, releasing heat - favourable in high temperatures
Genetic Drift
the random, non-directional change in allele frequency between generations
No selective agents, Non-directional
Why is genetic drift more likely to occur in smaller, genetically isolated populations
- This is because it is often a result of genetic bottleneck - results from inbreeding brough about by the limited mating possibilities in a small community
- Smaller the population size, the greater the potential impact of genetic drift
2 Extreme examples of genetic drift
Founders Effect + Bottleneck Effect
Founders Effect defintion + examples
- Where a new population is formed by a small number of individuals from an original population
- Can be caused by migration, of a smaller group or isolation due to barriers
5 Characteristics of new population in Founders Effect
- A different allele frequency from the original population
- Decreased genetic variation compared to the original population
- The small sample size of the new population is not a good genetic representation of the original population - marked deviations in allele frequencies
- The new population shows a frequency of features not typical of the original homeland population
- Certain alleles can be missing altogether from individuals in the isolated population
