Chapter 9 Flashcards
Gene Pool
The complete set of alleles present within a particular population.
Gene
Section of DNA that carries the code to make a protein.
Allele
Alternate form of a gene.
Population
Group of individuals of the same species living in the same location.
Allele frequency
Proportion of certain alleles in a gene pool.
Larger and more diverse allele pool =
- Greater gene variety + alleles.
- Therefore a greater number of genotypes and phenotypes.
- Increasing genetic diversity.
Genotype
Genetic compostion of an organism at a particular gene locus.
Phenotype
An organism’s Physical or biomedical characteristics result from gene expression and the environment.
Genetic diversity.
Variation in genetic makeup or alleles within a population.
Mutations
Permanent change to a DNA sequence.
- Introduce new alleles into a population via changes to DNA.
- Spontaneous or Induced by Mutagens.
- Can be advantageous, neutral or deleterious.
Mutagens
An agent that can cause mutations in DNA.
Mutations cause:
Effect downstream expression of a particular gene, altering the folding and functioning of the resultant protein.
For mutations to be inheritable
Needs to occur in germline cells.
If occurs in somatic cells –> Non-inheritable.
Heritability
Transmission from parent to offspring
Germline cells
Cells involved in the generation of gametes in eukaryotes.
Somatic cells
Any cell in an organism that isn’t a germline cell.
Point mutations
Mutations that alter a single nucleotide in a DNA sequence.
- Silent mutations.
- Missense mutation.
- Nonsense mutation.
- Frameshift mutation.
Silent Mutation
Substitution mutation that has no effect on resulting amino acid. A nucleotide is substituted for another, changing the codon, still coding for the same amino acid. (no effect on protein).
Substitution of a single nucleotide which does not lead to a change in the amino acid sequence
Missense Mutation
Substitution mutation which codes for a different amino acid altering the primary structure of the polypeptide. (alters the function of proteins).
Substitution of a single nucleotide which changes the affected codon, leading to the production of a different amino acid
Nonsense mutation
Prematurely end translation of genes mRNA. Substitution of nucleotide –> causes the affected codon to become a STOP codon. Therefore polypeptide becomes too short; the gene isn’t completely translated.
Substitution of a single nucleotide leading to the production of a premature stop codon
Frameshift mutation
Addition/deletion of 1 or 2 nucleotides that alter the reading frame of nucleotides. All following codons and amino acids they code for are affected causing major disruptions to the structure/function of a protein.
Insertion or deletion of nucleotides affecting every codon from the point of mutation onwards
Block mutations
Mutations that affect large amounts of DNA or entire genes
Changes to large sections of DNA causing significant changes to DNA sequences.
- Duplications;
- Deletions;
- Inversions;
- Translocations;
Environmental selection pressures (ESP)
Select for individuals best adapted to a specific environment.(improves survivability) Promoting survival + passing on alleles through natural selection.
Natural selection
Selection of phenotypes most suited to overcome the environment with an increased chance of survival.
Organisms that are more suited to the environment
Have higher genetic fitness due to advantageous phenotype from certain alleles; more likely to survive + pass down alleles (generational).
Selective advantage
Organisms conferred with a beneficial allele increasing the chance of survival against ESP.
4 conditions to facilitate natural selection
Variation; Vary genetically in pop.
Selection pressure; ESP impacts the survivability of organisms + ability to reproduce in pop.
Selective advantage; Phenotypes more fitter to ESP are conferred a selective advantage; to survive + reproduce.
Heritability; advantageous is to be passed from parents, freq of advantage increases.
Effect of selection pressures on genetic diversity
ESP decreases the genetic diversity of a gene pool. Fitter individuals with advantageous phenotypes are more likely to survive + reproduce.
Greater genetic diversity =
A higher chance of possessing a favourable allele means survival.
Low genetic diversity =
Risk of extinction. The inability to adapt to changing ESP.
Darwins observations.
- Phenotypic variation within speices is due to genotypic variation.
- Offspring tend to inherit traits of their parents.
- Species produce more offspring that required to replace themselves.
- Struggle to survive.
Darwin inferences (work on)
Traits w/ more chance of survival = more offspring.
Sexual selection.
“Female Choice”
- Reproduction above survival.
- Tournament species; usually males fight with each other for the right to mate with all females.
Genetic drift
Changes in a pop’s allele freq due to sudden/random occurrences; which effect genetic diversity.
Occurs via:
- Bottleneck effect.
- Founder effect.
Bottleneck effect
Occurs when a large portion of a pop is wiped out by a random event, decreasing pop size & genetic diversity. (Alleles are lost).
Founder effect
Occurs when a small unrepresentative sample of individuals separates from a large population to colonise a new region and start a new population.
Effect of genetic drift on genetic diversity
Both decrease genetic diversity; removal of alleles from gene pools.
Bottleneck –> Reduces genetic diversity via removal of alleles.
Founder –> Reduce genetic diversity through the establishment of new pop w/ a small unrepresentative sample of the original pop.
2 major risks of reductions in genetic diversity
- Interbreeding; harmful alleles in a gene pool.
- Lower adaptive potential; vulnerable to new selection pressures; could wipe out entire population due to absence of advantageous alleles.
Gene flow
Removal/Introduction of alleles between populations through migration/interbreeding.
- Populations in different geographic locations can exchange alleles via migration/interbreeding.
Immigration
Alleles are added to the gene pool.
Emigration
Alleles are removed from the gene pool.
Effect of gene flow on genetic diversity.
Introduce/remove alleles from a population, increasing/decreasing genetic variation.
Immigration –> increased genetic diversity of gene pool.
Emigration –> decreased genetic diversity of gene pool.
Speciation
Populations genetically diverge until they become distinct species } breed + produce viable(survivable) offspring.
Subspecies
Phenotypically different from the original population arise.
To indicate if they’re the same species
compare genetic composition; analyse amino acid sequences + DNA sequences; compare structural features.
Hybrids
Different species can breed to form hybrids but the offspring is infertile.
2 types of speciation
Allopatric + Sympatric
Allopatric speciation
Formation of new species as a result of a geographical barrier.
It isolates populations preventing gene flow between them and allowing genetic differences to accumulate; due to selection pressures.
Process of allopatric speciation
- Geographical barrier separates population; preventing gene flow.
- Different selection pressures favour different phenotypes.
- Genetic differences accumulate so 2 populations can no longer interbreed + produce viable & fertile offspring.
Sympatric speciation
Formation of a new species in the same geographical location.
eg. Howea Palm.
- Difference in pH of the soil on the island; causing plants to flower at different times, and experiencing different selection pressures; genetic differences then accumulate.
- They become different enough that they can’t interbreed.
Selective breeding
Humans can select or remove particular traits from a population by controlling the breeding of animals/plants with natural selection.
Artificial
Requirement for selective breeding
Variation; Individuals in pop vary genetically; phenotype differences.
Selection pressures; Direct human intervention puts artificial selection pressures on the population so they can breed with desirable traits.
Heritability; Traits need to be passed from parents to offspring.
Effect of selective breeding on genetic diversity.
Lead to smaller gene pools + overexpression of deleterious alleles decreasing adaptivity + fitness in a population.
Decrease in genetic diversity = Increased interbreeding + deleterious. Decreased adaptive potential.
Bacterial resistance to antibodies
Inappropriate use of antibodies lead to antibiotic-resistant bacteria.
Antimicrobial agent
Kills/slows the growth of microorganisms.
Antimicrobial resistance
Microorganisms’ ability to survive exposure to an antimicrobial agent.
Antibiotic resistance
An environmental selection pressure
Bacteria resistant to a particular antibiotic present in a population will be conferred a selective advantage and continue replicating.
Bacteria exchange genetic material via bacterial conjugation –> spreading alleles for antibiotic resistance.
Factors contributing to antibiotic-resistant bacteria:
- Inappropriate compliance with a treatment plan.
- Inappropriate use of antibiotics when not required.
Viral antigenic drift and shift
Modifies surface; increasing the difficulty of forming effective vaccines against viruses.
Drift:
- Small gradual changes (mutations) in genes coding for viral surface antigens.
Shift:
- Sudden and significant changes (mutations) in genes coding for viral surface antigens.
The Common Cold:
Rhinovirus.
High ability of surface antigens, constantly mutating therefore universal vaccine/antiviral development against the cold is very difficult.
Cannot form immunological memory.
