Evolution
Cambridge A-Level Biology (9700) · Unit 17: Selection and evolution · 7 flashcards
Evolution is topic 17.3 in the Cambridge A-Level Biology (9700) syllabus , positioned in Unit 17 — Selection and evolution , alongside Natural and artificial selection. In one line: Evolution is the change in allele frequencies within a population's gene pool from one generation to the next. This occurs due to various mechanisms like natural selection, genetic drift, mutation, and gene flow, ultimately leading to the formation of new species over time.
Marked as A2 Level: examined at A Level in Paper 4 (A Level Structured Questions) and Paper 5 (Planning, Analysis and Evaluation). It is not tested on the AS-only papers (Papers 1, 2 and 3).
The deck below contains 7 flashcards — 2 definitions and 5 key concepts — covering the precise wording mark schemes reward. Use the 2 definition cards to lock down command-word answers (define, state), then move on to the concept and calculation cards to handle explain, describe, calculate and compare questions.
Evolution in the context of population genetics
Evolution is the change in allele frequencies within a population's gene pool from one generation to the next. This occurs due to various mechanisms like natural selection, genetic drift, mutation, and gene flow, ultimately leading to the formation of new species over time.
What the Cambridge 9700 syllabus says
Official 2025-2027 spec · A2 LevelThese are the exact learning outcomes Cambridge sets for this topic. The candidate is expected to be able to do each of these on the relevant paper.
- outline the theory of evolution as a process leading to the formation of new species from pre-existing species over time, as a result of changes to gene pools from generation to generation
- discuss how DNA sequence data can show evolutionary relationships between species
- explain how speciation may occur as a result of genetic isolation by: • geographical separation (allopatric speciation) • ecological and behavioural separation (sympatric speciation)
Cambridge syllabus keywords to use in your answers
These are the official Cambridge 9700 terms tagged to this section. Mark schemes credit responses that use the exact term — weave them into your answers verbatim rather than paraphrasing.
Tips to avoid common mistakes in Evolution
- › Refer to them as 'populations of the same species' until reproductive isolation is established and they can no longer interbreed.
- › Identify speciation occurring within the same geographic area as 'sympatric speciation', often caused by behavioral or temporal isolation.
- › Clearly state that mutations are random; selection pressures only determine which existing alleles have a selective advantage in the environment.
- › Read the context carefully; for stem elongation, focus on how active GA leads to the breakdown of DELLA proteins, allowing PIF to bind to promoters.
- › Define low genetic variation as a small number of alleles existing at a gene locus within a population, regardless of their frequencies.
Define evolution in the context of population genetics.
Evolution is the change in allele frequencies within a population's gene pool from one generation to the next. This occurs due to various mechanisms like natural selection, genetic drift, mutation, and gene flow, ultimately leading to the formation of new species over time.
How can DNA sequence data be used to infer evolutionary relationships between species?
By comparing DNA sequences, scientists can identify similarities and differences between species. The more similar the DNA sequences, the more recently the species shared a common ancestor. Mutations accumulate over time, providing a molecular clock to estimate divergence times.
Describe allopatric speciation and give an example.
Allopatric speciation occurs when populations are geographically separated, preventing gene flow. Over time, the isolated populations accumulate different mutations and adaptations, leading to reproductive isolation and the formation of new species. Darwin's finches on the Galapagos Islands are a classic example.
Explain how ecological separation can lead to sympatric speciation.
Ecological separation, a form of sympatric speciation, occurs when populations in the same geographic area occupy different niches or habitats. This can lead to disruptive selection favoring different traits, ultimately reducing gene flow and leading to reproductive isolation. Apple maggot flies, which now specialize on different host plants (apples vs. hawthorns), demonstrate this.
Describe how behavioral separation can lead to sympatric speciation.
Behavioral separation, another form of sympatric speciation, involves differences in courtship rituals or mating preferences within a population. These differences can reduce gene flow between groups, eventually leading to reproductive isolation and the formation of new species. Different mating songs in some species of insects is an example.
What is the role of genetic isolation in speciation?
Genetic isolation is crucial because it prevents gene flow between populations. This allows for independent evolutionary trajectories, leading to the accumulation of genetic differences that eventually result in reproductive isolation and the formation of new species.
Outline the theory of evolution.
The theory of evolution proposes that all life on Earth has descended from a common ancestor through a process of descent with modification. This occurs via changes in the gene pool of a population from generation to generation, driven by mechanisms like natural selection, genetic drift, mutation, and gene flow.
More topics in Unit 17 — Selection and evolution
Evolution sits alongside these A-Level Biology decks in the same syllabus unit. Each uses the same spaced-repetition system, so progress in one informs the next.
Key terms covered in this Evolution deck
Every term below is defined in the flashcards above. Use the list as a quick recall test before your exam — if you can't define one of these in your own words, flip back to that card.
How to study this Evolution deck
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