U4T2 - Evolution | Lucas Flashcards
Be sigma
What is microevolution?
- Small scale variation of allele frequency
- Occurs within a species or population (Therefore does not form a new species)
What is macroevolution?
- Large scale variation of allele frequencies
- At or above the species level
- Occurs over geological time
- Results in divergence of taxonomic groups.
- Caused by an accumulation of microevolutionary changes.
What is evolution?
(The cool definition)
- Change in genetic composition of a population
- Occurs over successive generations
- May result in a new species.
What is comparative genomics and how is it used?
- It is the comparison of genetic features to determine evolutionary relatedness.
- It is used in phylogenetics and comparing different species’ genes such as in:
- Multiple sequence alignment charts
- Phylogenetic trees
- Data matrix of differences
What is natural selection?
- Individuals with the most favourable phenotype have an increased chance of surviving and reproducing due to selection pressures.
- Compared to individuals with less favourable phenotypes.
What are selection pressures and what can they do?
- External factors that affect an organism’s ability to survive in a given environment.
- They drive evolution (Along with mutations) as they give a particular phenotype a survival advantage.
What are the two different allele frequency selections?
Positive selection
- Promotes the spread of beneficial alleles
- Allele frequency increases in the population
Negative selection
- Hinders the spread of damaging alleles
- Allele frequency decreases in the population
What is stabilising selection?
- When intermediate phenotypes are favoured over the extremes.
- Generally occurs over time when environmental conditions remain relatively unchanged.
- Results in the graph becoming more narrow in the middle.
What is directional selection?
- When one side of the bell curve is preferred
- Generally occurs over time when environmental conditions have changed allowing one phenotype an advantage.
- Shifts the graph towards one side.
What is disruptive selection?
- When the extremes of the bell curve are favoured over the intermediate phenotypes.
- Occurs over time when distinctly different phenotypes give an advantage due to minimised competition.
- Results in a lower middle and higher extremes on the graph.
How does mutation affect microevolution?
- Creates new genotypes without inheritance.
- Due to the changes in genotype, there are potentially new alleles introduced into a population.
Define gene flow
- Movement of genetic material between populations.
- Changes gene pools based on the emigration (Leaving), or immigration (Joining) of a population.
- This changing creates new allele variation.
Define genetic drift
- The random fluctuations of alleles in a population over time.
- Can occur when populations decrease for a period of time (Bottleneck and founder effect).
- More significant effect in small populations, where it can result in the loss of genetic diversity as alleles are lost from the gene pool.
How does genetic isolation influence gene flow?
- It isolates two populations from each other causing gene flow to stop between the two.
- Eventually the two groups may no longer be able to breed and produce viable and fertile offspring, making them considered separate species.
What is the geographic/spatial isolating mechanism?
Individuals separated by geographic features such as mountains, rivers, incompatible habitats (Two oak tree populations separated by a desert) or distance (Spatial).
What is the temporal isolating mechanism?
Individuals breed during different seasons of the year or different times of the day.
What is the behavioural isolating mechanism?
Individuals have different courtship patterns
What is the morphological isolating mechanism?
Individuals have different reproductive organs and structures, making mating physically impossible.
What are the postzygotic isolating mechanisms?
Hybrid inviability - Hybrid offspring are not viable and generally the offspring won’t survive the full gestation period.
Hybrid sterility - Hybrid offspring of two different species will be infertile.
What is allopatric speciation?
- Most common form of speciation.
- Occurs when a geographical barrier divides a population.
- It prevents individuals of separated populations from interbreeding.
What is parapatric speciation?
- When populations maintain a hybrid zone (Zone of contact) but the area is large with significant variation in habitat conditions.
- Frequently occurs when a new niche becomes available.
- Gene flow is possible but as it is a large population over a large range, individuals are more likely to breed with nearby individuals.
- Slight differences in environmental pressures from one end of the range to the other can result in localised allele variation.
What is sympatric speciation?
- Members have contact but due to temporal or behavioural isolating mechanisms reducing gene flow.
What is divergent evolution?
- The differentiation of distinctly different species/populations from a common ancestor.
- Isolated species and populations accumulate genetic differences.
- Example: Darwin’s finches
What is convergent evolution?
- The evolution of similar features in unrelated groups of organisms.
- Features that are similar to others which have evolved from different ancestors are termed analogous.
- Example: Australian sugar glider and American flying squirrel
