C8 Genetics, Evolution, + Immunity Flashcards
Locus
Position of a gene on a chromosome
Allele
Genes occupying the same locus on homologous chromosomes
Homologous
Similar chromosomes: have same gene sequence, a pair.
Usually one inherited from the father and one from mother.
Genotype
The set of genes possessed by an organism (e.g. BB, Ee, kk)
Phenotype
Visible characteristics/physical expression of the genes (e.g. blue eyes, curly hair)
Mitosis
Normal cell division
- produces somatic (body) cells
- no change in chromosome number ( stays 2n)
Meiosis
Reproductive cell division
- produces gametes (sperm/egg)
- change in chromosome number (2n to n)
Diploid
Normal chromosome number for each species (pairs, 2n)
Haploid
Half the chromosome number for each species (single, n)
Gamete
Sex cell
- sperm/egg
- haploid (n)
Zygote
Fertilised cell
- sperm + ovum combined
- 2n (diploid)
Pure breeding
Pedigrees
- organisms containing homozygous genes for a trait (BB/bb)
Homozygous
Identical genes in a pair (e.g. PP, tt)
Heterozygous
Different genes in a pair (e.g. Pp, Tt)
Dominant
The gene that masks the other gene in the organism’s phenotype
- written as capital letter (e.g. B, T)
Recessive
The gene that is masked by the dominant gene in the organism’s phenotype
- written as lowercase letter (e.g. b, t)
Co-dominant
Both genes are equally dominant (e.g. A and B blood groups)
Sex-linked inheritance
Traits carried on the X chromosome (more room)
- tend to be recessive
More common in males:
- males only have one: therefore there is no chance of it being masked if it is passed down
- less common in females due to 2x X chromosome
Sons do not share the phenotypes of their fathers:
- must take Y chrom from father
- if father has the trait, will not affect the son
Autosomal trait
Trait carried on the non-sex (autosomal) chromosomes
- 22 pairs of autosomal chromosomes in humans, 1 pair sex chromosomes
autosomal inheritance
- what is it
- dominant vs recessive qualities
Autosomal inheritance: trait is carried on the autosomal chromosomes (not X/Y)
DOMINANT
- affected individuals carry at least one dominant gene
- non affected individuals must be homozygous recessive (e.g. bb)
- does not skip generations (affected people will be in all generations)
- sometimes the exact genotypes will be unclear (label the possibilities, e.g. BB/Bb)
RECESSIVE
- affected individuals must be homozygous recessive (e.g. bb)
- can skip generations
- people can be carriers but not affected, due to presence of dominant gene
Mutation
Random change in a gene or chromosome that alters the way it controls development
Linkage
Genes are linked on the same chromosome (search up a pic if unsure)
Trait
A characteristic that can be passed down
Hereditary
The passing of traits to the next generation
Monohybrid cross
A cross involving a single trait (e.g. hair colour)
Dihybrid cross
A cross involving two traits (e.g. hair colour and eye colour)
simple/mendelian inheritance
occurance of a trait is controlled by a single gene
- dominant and recessive alleles
State the 3 generations used in genetics problems.
- P1 parental: og generation
- F1 filial: offspring from P1
- F2 filial: offspring from F1
Outline what needs to be stated when solving a punnett square problem.
- all possible genotypes
- all possible phenotypes
- offspring possibilities (percentage of geno/phenotypes occurring)
- genotypic ratio (e.g. 1:2:1)
- phenotypic ratio (e.g. 3:1)
NON-MENDELIAN INHERITANCE PATTERNS
Describe what occurs in the following scenarios:
- incomplete dominance
- co-dominance
INCOMPLETE DOMINANCE
- when the genotype is heterozygous, neither gene is recessive to the other
- neither phenotype is expressed fully
- results in a ‘blend’ of the two traits
- e.g. R red + r white = Rr pink flower
CO-DOMINANCE
- when the genotype is heterozygous, there is no dominant allele
- results in both traits being expressed simultaneously (spots, speckles, patches)
- alleles are different letters (e.g. B + G) or with a common letter with subscript (e.g. C^B + C^G)
Describe how there is co-dominance in human blood types:
- blood type phenotypes
- blood type genotypes
- how blood can be donated
PHENOTYPES
- type A (A antigens)
- type B (B antigens)
- type AB (A + B antigens)
- type O (no antigens, recessive)
GENOTYPES
A/B are codominant, but dominant over i recessive:
- A blood type: I^A, I^A, or I^A, i
- B blood type: I^B, I^B, or I^B, i
- AB blood type: I^A, I^B only
- O blood type: i, i only
DONATING BLOOD
- only give blood if it has antigens that are already in your blood type
- O: give to anyone, only receive O
- AB: give to AB, receive all blood types
- A/B: give to their own type and AB, receive own type and O
State what can be found from a pedigree (4).
- how traits are transmitted/inherited
- predicted probability of having an affected child
- if a trait is dom/recessive
- if a trait is autosomal or sex-linked
What characteristics of a pedigree chart display that the trait is X-linked recessive
- sons would be affected if mother is affected (pass on recessive X chromosome)
- affected daughter’s fathers must be affected (both daughters’ Xs must be recessive = father has recessive X)
Chromosome
Genetic information
- contained in nucleus as strands
- before cell divides: DNA condenses into chromosome shape
- males = X + Y
- females = X + X
Species
a group of living organisms that (most of time):
- are morphologically similar
- can produce fertile offspring with each other
binomial
the system for naming organisms consisting of two terms
- 1st: Genus (capital)
- 2nd: species
evolution
the process of culminative change in the heritable characteristics of a population
natural selection
the process in which organisms that have better adaptions will flourish
- organisms with beneficial traits suited to the enviro will survive, produce more offspring
- over time, the beneficial traits become more frequent
- by this process, species evolve to better suit their environment
State the 4 sections that need to be addressed when answering natural selection questions.
- there is genetic variation due to random mutation from sexual reproduction, leading to different traits (resulting in… state specific trait)
- not all organisms will reach maturity due to the selective pressure (state specific one)
- survival of the fittest: the organisms with the specific advantage (state) are able to… (state how trait gives advantage), and therefore survive at higher rates compared to organisms w/o it, and go on to reproduce more, passing the trait on to their offspring
- over time, the allele gene pool will change and the specific advantageous trait (state) will become more common
allele frequency
how common/the frequency at which specific alleles occur within a population
- changed by evolution/speciation/genetic drift
fertile
an organism that can produce offspring
morphologically similar
organisms that LOOK the same/have similar physical features
divergent vs convergent evolution
- Divergent: species diverge from a common ancestor and therefore have similar characteristics
- Convergent: species with different ancestors develop similar traits
speciation
- new species evolve when populations become isolated
- they evolve independently (due to random mutation and natural selection)
allopatric isolation
populations that are geographically isolated by a physical barrier
- have specific adaptations to a specific enviro
- over time, speciation occurs
sympatric isolation
- different types (4)
populations that are isolated in another way:
- Temporal: species breed at different times of the day/year (e.g. nocturnal)
- Behavioural: unique mating behaviors identifies a species and only attracts same species
- Mechanical: unique reproductive organs/methods prevent reproduction between populations
- Gametic: sperm cannot fertilise another species’ eggs (occurs in marine enviros)
post-reproductive barriers
The zygote develops, but:
- offspring are infertile and cannot go on to reproduce
- embryo cannot develop, dies before birth
- embryo is incompatible with the mother
hybridisation
the breeding of two similar but different species
- often infertile
- often weaker/less fit
rate of speciation
a debate about whether speciation is:
- gradualism: occurs gradually
- punctuated equilibrium: occurs rapidly
GENETIC DRIFT
- what is it?
- what is it caused by
- what does it do to a pop?
- more prominent in…
- describe the two ways in which it occurs
GENETIC DRIFT
- evolution that is caused by random/chance events
- not natural selection
- an event removes part of a pop: the new pop has a reduced + different gene pool, different to the source pop
- now diff alleles have a higher frequency of occurring, resulting in evolution over time
- speciation will likely occur if the population is geographically isolated
- results in more prominent change in small pop.s, due to small gene pool with less variation
FOUNDER EFFECT
- random event leads to the colonisation of a new area by a limited no. of individuals from a source pop
BOTTLENECK (DISASTER)
- random disaster leads to a large reduction in pop. size
- individuals survive by chance, not by having an advantageous trait
Describe the pros (4) and cons (4) of mitosis (asexual reproduction).
PROS
- time and energy efficient (allow rapid reproduction)
- advantageous traits guaranteed to be passed down
- can occur in wide variety of enviro conditions
- 1 organism can establish a population
CONS
- limited genetic diversity (clones, only source of variation is random mutation)
- negative traits guaranteed to be passed down
- change in enviro conditions can eliminate an entire pop (if no resistance)
- replication of defective cells can become uncontrolled (cancer)
Describe the pros (3) and cons (3) of meiosis (sexual reproduction).
PROS
- high genetic variability (from crossing over/ind. assortment)
- more adapted + protected from disease, defects and enviro change
- negative genetic traits are not guaranteed to be passed down
CONS
- not time or energy efficient (embryo development takes time = slow pop growth)
- requires 2x gametes from 2x different organisms
- requires favourable/safe conditions
types of disease
- non infectious
- infectious
non infectious
- cannot be transmissible (except genetically)
- not caused by a pathogen
- cause by: genetics, lifestyle, enviro, substance abuse
- e.g cancers, genetic disorders, diabetes, mental illness
infectious
- transmissible/communicable
- caused by the infection of a pathogen into blood/body fluids/cells
pathogen
disease causing agent
modes of transmission
- contact
- non contact
CONTACT
- pathogen is on organism/object (carrier)
- touched by organism directly
- Direct: physical contact between two organisms (touching, biting, intercourse, kissing), contact/exchange of body fluids
- Indirect: organism comes into contact w inanimate object (fomite) that pathogen is deposited on
- Droplets: organism comes into contact w infected body fluid within 1m of source, then inhaled
NON CONTACT
- Airborne: transmission via tiny droplets (aerosols), over 1m from source (e.g. flu, covid)
- Vehicle: food/water is contaminated (e.g. water borne viruses, food poisoning)
- Vector: another organism (animal/plant) is infected and carries pathogen
State the types of pathogen, what each is/how they work, and some examples. (6)
PRIONS
- altered/abnormal protein made in cell
- cells fill with them and burst, spreading to other cells and continuing production
- break down brain tissue
- no known treatments
VIRUSES
- ultramicroscopic
- piece of RNA/DNA wrapped in a capsid (protein coat)
- reproduce inside a host cell
- cell bursts, spreading to other cells
- treatments: antiviral reduces severity, vaccine reduces infection likelihood and severity
BACTERIA
- prokary cells (some pathogenic)
- reproduce by binary fission (fast asexual reprod)
- if harmful, can: destroy cells/tissues due to enzymes, produce waste toxins, exaggerate immune response to foreign cells
- treatment: antibiotics stop cells functioning
PROTOSOAN
- single celled parasite (some pathogenic)
- e.g. malaria
FUNGI
- eukary organisms (some pathogenic)
- made of network of fungi spores, spread easily
- thrive in moist dark conditions
MACROPARASITES
- multicellular organisms
- dependent on host for life cycle
- endo (live in host, e.g. worms, flukes) ecto (live on host, e.g. lice, ticks, fleas)
State the purpose for each of the 3 lines of defence.
- body’s immune system - defence against disease/pathogens, malfunctioning cells, foreign particles
First line
- prevents entry
- innate
- non-specific
- mechanical/chemical barriers
Second line
- after pathogen entry (body fluids/tissue/cells)
- innate
- non-specific
Third line
- creates defence to a pathogen that body previously exposed to
- adaptive (not innate)
- specific
FIRST LINE OF DEFENCE
- mechanical
- physical
- chemical
- biological
Mechanical (‘structural’)
- physically stop pathogen from entering body
- external: skin, hair (eyelashes, genitals, ears, nose)
- internal: mucous membranes (produce mucous that lines body tracts/openings, traps pathogens, cilia maneuver mucous up and out)
Physical
- attempt to expel pathogen from body systems
- coughing, sneezing, vomiting, urination, diarrhoea
Chemical
- acids/enzymes make conditions unfavourable
- tears, saliva, mucous, sweat
Biological
- good bacteria outcompete pathogens for space, and produce toxins that kill them
SECOND LINE OF DEFENCE
- blood lymph systems (functions of both)
- WBCs (2 types, which is 2nd line, phagocytosis?)
- inflammatory response (4 steps)
- fever
- chemicals (cytokines, complement proteins)
- NK cells
- clotting
BLOOD/LYMPH SYSTEMS
- responsible as transportation network for 2nd/3rd line of defence
- Blood: produces WBCs and transports to infection site
- Lymph: a network of lymph capillaries/vessels, interconnected w blood capillaries, filters out lymph (blood plasma), transports to lymph nodes + tissue around body, pathogens/damaged cells filtered out of body
WBCs
1. Phagocytes (2nd line)
- engulf + digest pathogens
- Phagocytosis: phagocytes move from blood to infection site, devour foreign materials by endocytosis
- Neutrophils: first on site, large numbers, die after phagocytosis
- Macrophages: made in bone marrow, mature + stay in lymph system
- Lymphocytes
- B + T lymphocytes (3rd line)
- NK cells (2nd line)
INFLAMMATORY RESPONSE
- body’s reaction when cells/tissue are damaged
1. Mast cells (in connective tissue) release histamines when damaged, which signal:
2. Vasodilation (increase blood flow) and increased permeability (increase fluid flow to site)
3. Phagocytes (neutrophils/macrophages) to area to engulf pathogens
4. = inflammation (area becomes swollen, hot, red)
FEVER
- triggered if pathogens enter body + cause lrg scale infection
Causes:
- increased body repair (increased metabolism)
- reduction of microbial multiplication (fever reduces iron lvls, bacteria need for reprod)
- slowing of pathogen replication (temp over optimum)
CHEMICALS
Cytokines
- chemical messengers
- produced by macrophages
- intensity inflammatory response by signalling 2nd line defence mechanisms
Complement proteins
- produced by liver
- inactive until pathogen is detected
- Aid response: increase inflammation, signal phagocytes to area, break down bacteria cell walls
- bind to pathogen (mark for destruction)
NK CELLS
- lymphocyte
- patrol body tissue
- do not attack pathogens, only body’s own cells if: they are cancerous, invaded by a virus
- recognise body cell as malfunctioning: induce apoptosis (programmed cell death), kill by release of harmful substance
CLOTTING
- chemical signals cause a mesh of fibres to form over the site of damage
- traps RBCs
- platelets become sticky, creating clot
- prevents blood loss and entry of pathogens
antigen vs antibody
Antigen
- specific proteins/polysacch.
- on outer surface of cells/viruses/released in bacteria toxins
- distinguish types of cell from another
Antibody
- large Y-shaped proteins
- produced by B-lymphocytes
- released into body fluids
- will only bind to specific antigen
THIRD LINE OF DEFENCE
- humoural response
- cell-mediated response
HUMOURAL RESPONSE
- pathogen is in body fluids (not inside cells yet)
- involves production of antibodies
B-Lymphocytes
- produced and mature in bone marrow
- have specific antibodies, match to specific antigen
- when this occurs, the cell is activated: rapidly clones, producing:
- Effector/plasma cells: produce specific antibodies
- B-memory cells: remember how to make the specific antibodies if reinfected
- Antibodies work by: making pathogens insoluble (cannot infect cells), clump together (easier phagocytosis removal), neutralise viruses (prevent attachment to cells), etc
CELL-MEDIATED RESPONSE
- pathogen is in body cells
- no antibody production in this stage
T-Lymphocytes
- produced in bone marrow, mature in thymus gland
- receptors detect MHC I from body cells that are infected by a pathogen (display antigen fragments)
- T cell clones itself, forming:
Helper T
- must be activated by antigen presentation (pathogen fragments on MHC II on APCs)
- activated helper T controls rest of immune response
- clones itself into all types of T cell
- releases cytokines (triggers other immune cells e.g. phagocytes, B-lymphocytes, inflammation)
- check and balance (identifies + activates correct B lymphocyte = cloning and antibody production)
Cytotoxic T
- destroys cells identified as non-self (missing MHC I, or displaying pathogen antigen fragments on MHC I)
- binds w infected cell to kill (injects toxins, cause cell lysis)
Memory T
- stay in lymph tissue until cells reinfected 2nd time
- if exposed to antigen again, allow faster + more effective recognition
Supressor/regulatory T
- turn off immune response/antibody production
- once infection has been checked
MHC markers
MHC I
- all body cells have on cell surface
- allow distinguishment between self/non-self cells to identify pathogens (absence/alteration of markers)
- allows pathogens to be marked for destruction
MHC II
- possessed by phagocytes after engulfing pathogen
- allows presentation of antigen fragments to lymphocytes (T/B cells)
- alerts body of foreign invader
antigen presentation
- APC (antigen presenting cells) present antigen fragments on MHC II
- activate T+B lymphocytes
- if body’s own cells: present pathogen’s antigens on MHC I, signals they are a threat + must be destroyed
IMMUNITY
- what is it and how does it happen?
- active vs passive
Immunity
- organism must undergo adaptive response (3rd line, making of memory cells)
- must be exposed to pathogen’s antigens
- upon 2nd infection: memory cells activate, provoking stronger immune response
= immunity
Active
- body undergoes adaptive 3rd line (antibody/memory cell production)
- long lived immunity (can take time to form)
- Natural: exposed to antigens, infected, recovers
- Artificial: exposed to antigens via vaccine
Passive
- body does not undergo adaptive 3rd line (NO antibody/memory cell production)
- short lived immunity
- Natural: antibodies received by baby from mother (milk/placenta)
- Artificial: infected person injected w antibodies to help fight disease
vaccines
contain:
- dead pathogens/antigens
- fragments of pathogens/antigens
- live but weakened pathogens
- mRNA (instructions to make pathogen’s antibodies)
