What is evolution?
Evolution is the change in the genetic composition of a population during successive generations, which may result in the development of new species
- microevolution
- macroevolution
What is microevolution?
Microevolution is the small-scale variation in allele frequencies within a population, where the descendants remain in the same taxonomic group as their ancestors.
It is driven by processes such as:
- Natural selection
- Mutation
- Genetic drift
- Gene flow
What is macroevolution?
Macroevolution is the variation in allele frequencies at or above the level of species over geological time, resulting in the divergence of taxonomic groups, where the descendants belong to a different taxonomic group from their ancestors.
What is evolutionary radiation?
An evolutionary radiation is a rapid increase in diversity of a clade, often resulting in the formation of many new species adapted to different ecological niches.
What is a clade?
- a clade is a grouping that includes all the descendants of a common ancestor
- The diversity of a clade is generally measured by its taxonomic richness, such as the number of species, genera, or higher taxa it contains
Impact of mass extinction?
- extinction is important in evolution because it provides opportunities, in the form of vacant niches, for the evolution of new species
- mass extinctions include those events that wipe out vast number of species in a brief period of time, there has been 5 major extinction events over the last 600 million years
What is comparative morphology?
Comparative morphology involves comparing the structures of living organisms and fossil evidence of extinct species, to infer evolutionary relationships.
What is homologous features?
Homologous features are structures that are similar in related organisms, because they were inherited from a common ancestor.
What is comparative embryology?
Comparative embryology is the study of the similarities and differences in the embryos of different species.
What is comparative genomics?
Comparative genomics is a field of biological research in which the genomic features of different species are compared to determine evolutionary relatedness.
What is Darwin’s idea of common descent?
Darwin’s idea of common descent explains that the diversity of life arises from a single ancestral origin, modified over time by evolutionary processes like natural selection.
What is Darwin’s theory of natural selection?
Natural selection is the process by which environmental pressures give certain phenotypes a selective advantage, increasing their chances of survival (viability) and reproduction (fecundity), causing that phenotype to become more common in subsequent generations.
What are gene pools?
A gene pool is the total set of all alleles (gene variants) present in a population at a given time.
Change to the gene pool occurs by 4 processes:
- mutation
- natural selection
- genetic drift
- migration (gene flow)
What is the process of natural selection?
- Variation:
- individuals in a population differ in traits (e.g., size, colour, behaviour). - Overproduction:
- more offspring are produced than can survive → leads to competition for resources. - Selection (Differential Survival & Reproduction):
- individuals with traits best suited to the environment survive and reproduce more successfully. - Inheritance:
- advantageous traits are passed to offspring. - Adaptation:
- over generations, these beneficial traits become more common, and the population becomes better suited to its environment.
Positive vs negative selection?
Positive selection favours a particular allele, resulting in an increase in its frequency.
Negative selection acts against a particular allele resulting in a decrease in its frequency.
The ‘strength’ of the selection pressure determines the degree to which the allele frequency changes within the population.
What are processes of microevolutionary change?
Mutations: changes to the DNA sequence can create new alleles. If favourable, they will become more common in the population.
Natural selection: over time, favourable phenotypes become more common in the population as they reproduce more.
Genetic drift: genetic drift causes microevolution by randomly changing allele frequencies in a population over time.
Migration (gene flow): through immigration or emigration, alleles can enter or leave the population.
What are the modes of phenotypic selection?
- stabilising selection: selection favours the intermediate phenotype
- directional selection: selection shifts to favour a slightly more or less phenotype
- disruptive selection: selection favours both extreme phenotypes
What is speciation?
Speciation is the process by which populations evolve through natural selection to become distinct species.
The new species can no longer interbreed with the ancestral population to produce fertile offspring.
What are the modes of speciation?
Speciation through natural selection can occur in 3 ways:
- allopatric
- sympatric
- parapatric
What is allopatric speciation?
Allopatric speciation occurswhen reproductive isolation is a direct result of the geographical separation of two (or more) populations.
The physical barrier, such as a river or mountain range, makes it impossible for the two populations to breed with one another (no gene flow).
What is sympatric speciation?
Sympatric speciation occurs when new species evolve without physical (geographic) barriers, with members of the population living in close proximity.
Reproductive isolation arises due to ecological, behavioural, or temporal differences, such as some individuals exploiting different resources or breeding at different times, preventing interbreeding.
What is parapatric speciation?
Parapatric speciation occurs when geographically adjacent populations evolve into distinct species, despite having a partial overlap (hybrid zone).
Individuals are more likely to mate with nearby neighbours than with individuals from distant parts of the population’s range.
Divergence arises due to reduced gene flow and different selection pressures across the population’s range.
What is genetic drift?
Genetic drift is the random change in allele frequencies in a population due to chance events (e.g. floods, eruptions), which can cause alleles to disappear and reduce genetic variation.
What is the founder effect?
The founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population
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Unit 3 - Topic 1 (Biodiversity)39
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Unit 3 - Topic 1 (Classification Processes)42
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Unit 3 - Topic 2 (Functioning Ecosystems)34
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Unit 4 - Topic 1 (DNA structure and replication)23
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Unit 4 - Topic 1 (Cellular replication and variation)25
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Unit 4 - Topic 1 (Gene expression)38
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Unit 4 - Topic 1 (Mutations)26
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Unit 4 - Topic 1 (Biotechnology)19
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Unit 4 - Topic 1 (Inheritance)15
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Unit 4 - Topic 2 (Evolution)31
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meiosis - cellular replication extra7
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gene expression - extra12
