evolution Flashcards
Allele
Gene
Proteins
Phenotype
Genotype
Allele: A variant of a gene; brown eyes, blue eyes, etc
Gene: sequences of DNA that code for a protein
Proteins: functional polypeptides
Phenotype: physical expression of a gene; eye colour, hair colour, blood type
Genotype: The genetic make-up of an organism that determines or contributes to the phenotype
What causes genetic mutation, it’s impact on genetic diversity, can our bodies fix bad mutations & kinds
**Genetic mutation **
- Can be caused by mutagens or randomly occur
- increases genetic diversity & can change the gene pool
- Our bodies have ways to fix DNA to avoid bad mutations
Kinds: of mutations
- Advantageous
- Neutral
- Deleterious: negative impact on individual fitness
Gene pool
How to determine whether evolution has occurred
How to have diversity
Gene pool = all of the alleles present in a population
–> Changes to the gene pool result in evolution
–> The greater the variation and number of alleles within a genetic pool, the greater the genetic diversity
- Define evolution
- link b/w changes to gene pools and evolution
- why evolution/change in gene pool may occur
Evolution = change in gene pool over time.
Changes in gene pool = evolution:
- random event [genetic drift]
- natural selection
- reproduction of mutations
- gene flow
- artificial breeding
Genetic diversity
define Genetic drift & state diff kinds
**Genetic diversity = **variation of alleles within a population
Genetic drift: A random event that dramatically alters a populations gene pool
- Bottleneck effect
- Founder effect
Founder effect
- Reduction in genetic diversity
- when a population is derived from a small unrepresentative sample of the original population
Bottleneck effect
- Reduction in genetic diversity
- occurs when a large proportion of a population is removed due to a chance event
Point mutations
- Base substitution
Point mutations: change 1 nucleotide; substitution, deletion or insertion.
Can be further differentiated into:
silent → doesn’t change the amino acid
- bc genetic code is degenerate so despite the change to the original DNA sequence the same amino acid is produced and incorporated into the protein
nonsense → codes for STOP codon
- pre-maturely ends the translation of a gene’s mRNA
- the gene will not be completely translated meaning the polypeptide will be too short to function properly
- most dangerous mutation
missense → changes one amino acid**
frameshift mutations
- Addition or deletion of a nucleotide that alters the reading frame [read in triplets/codons] of the following nucleotides
- causing a major disruption to the structure and function of proteins as it could alter the base sequence of a gene so that the message it encodes is no longer the right amino acid
- degenerate
- reading frame
- a single amino acid can be coded for by more than 1 codon
- the order in which nucleotide triplets [codons] are divided into consecutive non-overlapping sequences to be read and translated into amino acids
Block mutations & the diff types
- occur on a chromosome
- **Deletion: **removal of a section of DNA
- **Duplication: **replication of a section of DNA, lengthening the DNA
- Inversion: reversal of a section of DNA
- Translocation: switching of 2 different sections of DNA on diff chromosomes
Aneuploidy
- chromosomal abnormality where an organism has an incorrect number of total chromosomes due to the addition or loss of a chromosome
- can result when homologous chromosomes fail to segregate in anaphase of meiosis stage I or when sister chromatids fail to segregate in anaphase of mitosis or meiosis stage II
- additional chromosome on the 21st gene causes Down syndrome
- turner’s syndrome 1 x chromosome instead of 2
Polyploidy
- a change in the number of sets of chromosomes
- most species are diploid -> 2 sets of chromosomes
- some species have more than two sets of chromosomes -> polyploid (eg. 3 sets of chromosomes (3 of each chromosome)
- can occur naturally through crossbreeding/hybridisation or can be induced using chemicals
hardy-weinberg equilibrium
In large, randomly mating populations where there are:
- no mutations
- no migration
- all phenotypes are equally suited to the environment
there will be no change in allele frequencies
→ gene pool/allele stability
→ no evolution (remain the same)
natural selection
natural selection = a mechanism through which organisms that are better adapted to their environment have an increased chance of surviving and passing on their alleles
- these traits are already present in the population
- can cause an increase or decrease in gene diversity
- selection pressures lead to natural selection
- natural selection occurs when any selecting agent acts on a population creating a selective advantage [when selective agents create a selective advantage]
- the differences in survival and reproduction result in changes to allele frequencies
- –> results in evolution
outline the steps involved in natural selection
- Varitation
* there is heritable phenotypic variation b/w members in a population. - selection pressure
* A specific environmental selection pressure causes a struggle for survival. - trait w/ selective advantage
* Members with advantageous alleles have increased chances of surviving and reproducing - Heritability
* These “fitter” organisms thus have higher chances of passing on their advantageous alleles to their offspring,** increasing those allele frequencies over successive generations**
* can only be inherited if the trait mutates in the germline cells
Population
Allele frequency
Population = a group of individuals of the same species living in the same location
Allele frequency = The proportion of certain alleles in a gene pool
mutations as a source of variation
generally, the genetic material of an organism is stable both in its base sequence and in its chromosomal location and is passed unchanged from generation to generation
- mutations are changes in the DNA sequence
- can be small → changes to nucleotides (point)
- can be larger → changes to sections of chromosomes (block)
Inbreeding
Adaptive potential
Inbreeding - Sexual reproduction b/w 2 related individuals
–> keeps harmful alleles in the gene pool
Adaptive potential - The ability for a population to adjust to new environmental selection pressures
–> Lower adaptive potential: Populations become vulnerable to new selection pressures that could challenge and potentially wipe out the entire population due to the absence of advantageous alleles
Interbreeding
-> Gene flow
-> Immigration
Emigration
Gene flow - The flow of alleles in and out of a population due to the migration or interbreeding of individuals b/w 2 populations
–> Interbreeding - When 2 individuals living in different populations mate and have offspring
–> Immigration - The movement into a population
Emigration - The movement out of a population
Category & effect on genetic diversity of these mechanisms:
- Genetic drift: 2
- Gene flow: 3
Genetic drift:
examples of chance events:
* destruction of habitat
* drought
* bushfire
* introduced diseases
- Bottleneck effect: Decrease genetic diversity
- Founder effect: Decrease genetic diversity
Gene flow
- Immigration: Increase genetic diversity
- Emigration: Decrease genetic diversity
- Interbreeding: Increase genetic diversity
Define
- Selective breeding/artificial selection
The changing of a population’s gene pool due to humans altering the breeding behaviour of animals and plants to develop a selected trait
The effect of selective breeding on genetic diversity
- can lead to smaller gene pools
–> overexpression of deleterious alleles, reducing adaptability and fitness within a population as it also lowers adaptive potential. - can cause a human-induced genetic bottleneck
mechanism of artificial selection
- there is heritable phenotypic variation within the population’s gene pool
- humans select individuals with a desired trait
- humans alter the breeding behaviour of these individuals to breed (reproduce) and pass specific alleles onto the next generation
- the alleles that lead to the desired phenotype will be inherited by subsequent generations and they can increase in frequency in the gene pool over time
1. variation
2. selection pressure
3. favoured trait & heritability
antibiotic resistance is due to:
- patients not finishing an entire course of antibiotics
- increased use of antibiotics in livestock farming; enables antibiotic ingestion by humans
- misuse of antibiotics e.g. prescription of antibiotics on non-bacterial related infections
- doctors overprescribing antibiotics
- lack of infection control in medical centres
- poor hygiene and sanitation
Viral antigenic evolution: Antigenic drift and shift
Antigenic drift: when a point mutation alters a virus’s nucleic materials resulting in small changes to its antigens until the accumulation causes the antigen to be unrecognisable
**Antigenic shift: **occurs when two or more strains of a virus combine to form a new strain of the virus with antigens from each of the original strains
- Antigenic shift often occurs when a species is infected with more than one strain of a virus
Darwin vs Lamark’s theory
**Darwin: **Giraffes with short neck die, giraffes with long neck pass on the trait
Lamarck: physical changes in organisms during their lifetime - such as greater development through increased USE, could be transmitted to their offspring.
treatments: virus
Rest
Hydration
Antivirals
(vaccines)
factors affecting a populations gene pool
Gene pools tend to remain constant (unchanging)
Unless something acts to change the gene pool
- mutation
- selection (natural or sexual)
- random events (genetic drift)
- gene flow (emigration and immigration)
- human intervention
selection pressures
[- selection pressures can select for or against phenotypes
- selection pressures act on the phenotype and change the genotype (gene pool - allele frequencies)]
selection pressure = an external agent which affects an organism’s ability to survive in a given environment
physical - climate change, shelter, food availability
biological - competition, predators, disease
chemical - pollutants, drugs (antibiotics)
change in population equation
change in population = births - deaths + immigration - emigration
impact of events on genetic diversity
natural selection → decrease in genetic diversity
- during natural selection, a particular phenotype has a selective advantage so particular alleles become more common, while others are removed
gene flow → increase in genetic diversity
- usually, the movement of alleles results in new alleles coming into a population
genetic drift → decrease in genetic diversity
- random chance events may lead to a loss of alleles in a population
bottleneck → decrease in genetic diversity
- event leading to the death of many members of a population may lead to a loss of alleles in a population
founder effect → decrease in genetic diversity
- the population is descended from individuals with limited diversity in their genetic material
mutations → increase in genetic diversity
- mutations are the source of new alleles
outline the process/formation of antibiotic resistance
- heritable phenotypic?genetic? variation exists b/w bacterium in a population, with some having advantageous alleles that confer antibiotic resistance.
- an antibiotic acts as an environmental selection pressure, when the antibiotic is added antibiotic-resistant bacteria have a selective advantage and increased chances of surviving and passing on their advantageous alleles via binary fission or bacterial conjugation
- allele frequencies of those advantageous alleles increase over successive generations and an antibiotic resistant bacterial population has formed
consequences of bacterial resistance
- more challenging to treat common infectious diseases
- normally treatable diseases can now be life-threatening if they have an antibiotic-resistant strain of bacteria
—> eg. pneumonia, tuberculosis, gonorrhoea, salmonella - WHO sets up the Global Antimicrobial surveillance system to monitor antibiotic resistance
—-> solutions: - new antibiotics –> which bacteria aren’t resistant to
- new treatment options
- time length of treatments being altered
mutations of viruses
viruses mutate at a high rate during replication and antigens can change
- especially for viruses that have RNA as their nucleic material - no proofreading mechanisms like enzymes that check for mutations in RNA as compared to DNA
—> eg, influenza, stars cov 2, HIV, ebola - the degree to which the antigens are altered will result in either antigenic drift or antigenic shift
consequences of antigenic drift and antigenic shift
no mutation of virus (same strain)
- full immune response immediately
- B memory cells produce antibodies quickly
- no illness
antigenic drift of influenza
- partial immune response
- B memory cells can produce antibodies and can form SOME antibody-antigen complexes
- no illness
antigenic shift of influenza
- immune system has no memory of pathogen
- time required for adaptive immune response
- illness
constantly mutating therefore a single vaccination cannot be made and administered to provide long-term protection
Australian government make a vaccine covering the most common seasonal strains of influenza for each year
State 3 differences between natural selection and selective breeding
**natural selection: **
1. occurs slowly over numerous generations
2. selected traits increase the chance of survival for the species
3. occurs due to environmental selection pressures
Artificial selection:
1. humans are the selection pressure
2. selected traits may not be advantageous for the organism
3. occurs faster as humans intervene
Compare natural selection to genetic drift
- natural selection selects for favourable traits while genetic drift occurs randomly due to chance events
- natural selection occurs over a long period of time, and genetic drift can occur as quick as over one generation
Describe how changes in the antigenic properties of viruses can lead to ineffective vaccines
Vaccine target the specific strain of virus (the antibodies produced from the stimulation of the vaccine aren’t specific to that strain)
mutation is a source of variation, explain
define mutation, these random mutations can result in changes to amino acid sequences coded by DNA which results in phenotypic variation
define mutation
random changes in DNA sequence
