Why can individuals within the same species show a wide range of phenotypic variation?
Genetic and environmental factors
Genetic variation (e.g. mutations, meiosis) and environmental influences both affect phenotype.
What is the primary source of genetic variation in populations?
Mutation
Mutations create new alleles and are the ultimate source of genetic variation.
How does meiosis increase genetic variation in sexually reproducing organisms?
Independent assortment and crossing over
These processes shuffle alleles during gamete formation, producing genetically different gametes.
Why does sexual reproduction generate more genetic variation than asexual reproduction?
Random fertilisation of gametes
Fusion of genetically different gametes produces unique allele combinations in offspring.
True or False:
Predation, disease and competition for resources can act as selective pressures in populations.
True
These factors affect survival and reproduction, driving natural selection.
What process describes the differential survival and reproduction of individuals with advantageous phenotypes?
Natural selection
Individuals with beneficial traits are more likely to survive and reproduce.
What happens to favourable alleles in a population when individuals with advantageous phenotypes reproduce more successfully?
Increase in allele frequency.
Successful individuals pass their alleles to offspring, changing the gene pool.
What term describes the collection of all alleles present in a population?
Gene pool
Evolution involves changes in allele frequencies within this pool.
How is evolution defined in genetic terms?
Change in allele frequencies in a population.
Evolution occurs over generations within populations.
What type of selection occurs when individuals with the average phenotype have the highest fitness?
Stabilising selection
Reduces variation and favours intermediate phenotypes.
What type of selection occurs when one extreme phenotype is favoured over others?
Directional selection
Causes the population mean to shift toward one extreme.
What type of selection occurs when both extreme phenotypes are favoured over the intermediate phenotype?
Disruptive selection
Can increase variation and potentially split populations.
True or False:
Natural selection can lead to changes in both phenotype frequency and allele frequency in a population.
True
Selection acts on phenotypes but changes underlying allele frequencies.
What process occurs when populations become unable to interbreed and produce fertile offspring?
Speciation
This marks the formation of new species.
What is required before two populations can evolve into separate species?
Reproductive isolation
Isolation prevents gene flow between populations.
What type of speciation occurs when populations become geographically separated?
Allopatric speciation
Physical barriers such as mountains or oceans isolate populations.
What type of speciation occurs when new species arise without geographic separation?
Sympatric speciation
Often due to ecological, behavioural or genetic isolation.
Why can isolated populations gradually develop different gene pools?
Accumulation of different mutations and selection pressures.
Without gene flow, allele frequencies change independently.
True or False:
Members of different species can always produce fertile offspring together.
False
Species are defined by their inability to interbreed to produce fertile offspring.
What process can cause random changes in allele frequency in a population?
Genetic drift
Changes occur due to chance rather than selection.
Why is genetic drift more significant in small populations than large ones?
Chance has a greater effect on allele frequencies.
Random events can drastically change allele frequencies in small populations.
How can evolutionary change over long periods contribute to biodiversity?
Accumulation of speciation events
Repeated divergence leads to many different species over time.
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3.1.1 Monomers & Polymers9
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3.1.2 Carbohydrates22
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3.1.3 Lipids17
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3.1.4 Proteins39
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3.1.5 Nucleic Acids32
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3.1.6 ATP11
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3.1.7 Water11
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3.1.8 Inorganic ions8
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3.2.1 Cell structure52
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3.2.2 Cell division20
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3.2.3 Transport across cell membranes20
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3.2.4 Cell recognition & the immune system36
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3.3.1 Surface area to volume ratio13
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3.3.2 Gas exchange24
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3.3.3 Digestion & absorption16
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3.3.4 Mass transport39
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3.4.1 DNA, genes & chromosomes13
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3.4.2 DNA & protein synthesis14
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3.4.3 Genetic diversity & meiosis14
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3.4.4 Genetic diversity & adaptation20
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3.4.5 Species & taxonomy20
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3.4.6 Biodiversity within a community12
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3.4.7 Investigating diversity12
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3.5.1 Photosynthesis23
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3.5.2 Respiration17
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3.5.3 Energy & ecosystems20
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3.5.4 Nutrient cycles15
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3.6.1 Stimuli & Response62
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3.6.2 Nervous coordination53
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3.6.3 Skeletal muscles14
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3.6.4 Homeostasis57
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3.7.1 Inheritance12
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3.7.2 Populations15
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3.7.3 Evolution may lead to speciation22
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3.7.4 Populations in ecosystems24
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3.8.1 Gene Mutations and Protein Structure14
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3.8.2 Control of Gene Expression44
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3.8.3 Applications of Genome Projects10
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3.8.4 Gene Technologies and Their Applications46
