Evolution & Natural Selection
Define Evolution
Change in the genetic composition of a population during successive generations, which may result in the development of new species
What are the three main types of phenotypic selection
Stabilising
Directional
Disruptive
Define Microevolution
Small-scale variations of allele frequencies within a species or population, in which the descendant is of the same taxonomic group as the ancestor
Explain speciation
The formation of new and distinct species in the course of evolution.
Identify the four patterns of diversification
Divergent Evolution
Convergent Evolution
Parallel Evolution
Co Evolution
Identify 2 environmental selection pressures
Climate conditions - flood, drought, extreme temperature changes
Competition for resources - availability of food and water, shelter and mate availability
This type of selection favours individuals with traits at one extreme of a range
Directional Selection
Give an example of microevolution
Peppered Moths: The frequencies of dark coloured moths increased in polluted environments as they were better camouflaged
Identify the 3 modes of speciation
Allopatric
Sympatric
Parapatric
Define Macroevolution
The variation of allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, in which the descendant is in a different taxonomic group to the ancestor.
What does a phylogenetic tree show?
An evolutionary relationship that exists between a group of species
Outline the four main requirements for natural selection to occur in a population
Variation: Variation in all traits exist due to genetic mutations – some variations are more favourable than others
Environmental pressure: The struggle for survival amongst individuals competing for resources will favour those with the most favourable variations.
Reproduction: The organisms best suited to the environment will have more offspring and pass on their favourable genes.
Allele Frequency: Over many generations, the gene pool of the population slowly changes to better suit the current environment.
Identify the four microevolutionary processes which can contribute to genetic change in populations
1. Mutation
2. Natural Selection
3. Genetic Drift
4. Gene Flow
Identify the type of speciation that occurs due to habitat fragmentation
Allopatric Speciation
Identify the 4 mechanisms of isolation
Geographic
Reproductive
Spatial
Temporal
An allele reduces an organism’s fitness, causing it to become less common in the gene pool, is this an example of positive or negative selection
Negative Selection
Traits that increase viability and fecundity are favoured by this process.
Natural Selection
Compare genetic drift and gene flow in microevolution
Genetic drift is the random change in allele frequencies whereas gene flow is the movement of alleles between populations.
Genetic drift: occurs in small populations of when a large population is reduced
Gene flow:results in immigration and emigration, increases genetic variation
Explain the founder effect
Occurs when a few individuals carry alleles to a new, isolated area and a new population is formed with different allele frequencies from the original population.
Less genetic diversity than the original population
Explain parallel evolution
Bonus points: Provide an example
Parallel evolution occurs when related species with a common ancestor independently evolve similar traits, often due to similar selective pressures, such as the Australian sugar glider and the North American flying squirrel evolving gliding membranes.
After a period of mass extinction follows a period of an increase in taxonomic diversity or morphological disparity. This is known as ...
Evolutionary Radiation
Explain how natural selection acted on finch populations to produce different beak shapes adapted to different food sources.
Natural selection acted on finch populations by favouring individuals with beak shapes suited to specific food sources. Finches with beak shapes that allowed them to efficiently access available food (e.g., large, strong beaks for cracking seeds or long, narrow beaks for probing cactus flowers) had a higher survival (viability) and reproductive success (fecundity). Over generations, these advantageous traits increased in frequency, producing populations with different beak shapes adapted to their particular diets.
Explain why small populations are more strongly affected by genetic drift than large populations
Small populations are more affected by genetic drift because random changes in allele frequencies have a greater impact when there are fewer individuals. In large populations, the effects of chance events are less, so allele frequencies remain more stable.
A population of 20 green and 5 yellow beetles live in a small patch of forest. A storm floods part of the habitat and randomly washes away many beetles. By chance, most of the green beetles are lost. What type of microevolution is this an example of?
Genetic drift (Bottleneck Effect)
Example Response:
This is an example of genetic drift, specifically a bottleneck effect, because a random event (flood) drastically reduced the population size. By chance, more green beetles were lost, so the allele frequency of yellow increased in the surviving population. This reduces genetic variation and may affect future evolution.
Give one example each of geographic isolation and explain how it can reduce gene flow between populations.
Geographic: Water bodies, mountains, deserts
Physical barriers prevent species from exchanging genetic material reducing gene flow between populations. This separation allows the populations to diverge genetically over time due to separate evolutionary pressures like natural selection and genetic drift, potentially leading to new species.