WACE Biology · Unit 3
Changes in a Population's Genetic Makeup
WACE Biology ATAR Unit 3 Continuity of species includes Continuity of life on Earth — how life has persisted, changed and diversified over about 3.5 billion years, and how the genetic makeup of populations changes. These 20 free flashcards and 20 true/false quiz questions cover the evidence for evolution (comparative genomics, comparative studies of proteins, the fossil record, comparative anatomy and embryology), phylogenetic trees, mutation as the ultimate source of variation, natural selection and selection pressures, the causes of change in gene pools (mutation, selection, genetic drift including the founder effect, and gene flow), allopatric speciation and reproductive isolation, macro-evolution from accumulated micro-evolution, selective breeding, and why populations with reduced genetic diversity face a higher risk of extinction. Aligned to the SCSA Biology ATAR Year 12 syllabus.
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Key Terms
- Gene Pool
- The total of all alleles of all genes in a population. Its allele frequencies change through mutation, selection, genetic drift and gene flow.
- Natural Selection
- The process by which a selection pressure gives individuals with a particular phenotype a selective advantage in survival and reproduction, increasing the frequency of the alleles responsible over generations.
- Genetic Drift
- Random change in allele frequencies due to chance, with the greatest effect in small populations. The founder effect and the bottleneck effect are examples.
- Gene Flow
- Movement of alleles between populations through migration and interbreeding. It makes the gene pools of populations more similar.
- Allopatric Speciation
- Formation of new species after a population is split by a geographical barrier and the isolated groups diverge under differing selection pressures until they are reproductively isolated.
- Phylogenetic Tree
- A branching diagram, built from protein, genomic and/or anatomical information, showing evolutionary relationships between groups; each node represents a common ancestor.
Sample Flashcards
Q1: How long has life existed on Earth, and what does the evidence show about how it has changed?
Life has existed on Earth for approximately 3.5 billion years. The earliest evidence is of simple prokaryotic (single-celled) life. Over time life has changed and diversified: eukaryotic cells, multicellular organisms and the major groups of plants and animals appeared progressively, while many groups have become extinct. The same processes that cause small changes in populations today, acting over this immense time, account for this diversity.
Q2: How does the fossil record provide evidence for evolution?
The fossil record documents the history of life by preserving remains or traces of organisms in sedimentary rock. It shows: 1) a progression from simple to complex organisms over geological time, 2) transitional fossils linking major groups, 3) the appearance and extinction of species. Radiometric dating provides absolute ages of fossils.
Q3: Explain how comparative anatomy provides evidence for evolution.
Comparative anatomy compares body structures across species. Homologous structures have the same basic structure but may have different functions (e.g. the forelimbs of humans, whales and bats), indicating inheritance from a common ancestor. Vestigial structures are reduced remnants of structures that were functional in ancestors (e.g. whale pelvic bones). Analogous structures do a similar job but have a different structure (e.g. bird and insect wings) — they reflect similar selection pressures, not common ancestry.
Q4: How does comparative embryology provide evidence for evolution?
Comparative embryology compares the early developmental stages of different organisms. Embryos of related vertebrates look very similar in early stages — for example, all vertebrate embryos have pharyngeal arches (pouches) and a post-anal tail at some stage — even though these features develop into very different structures in the adults. Shared developmental patterns suggest the organisms inherited the same developmental genes from a common ancestor.
Q5: What is comparative genomics, and how have new technologies added to the evidence for evolution?
Comparative genomics compares DNA sequences (genes or whole genomes) between species. The more similar the sequences, the more recently the species shared a common ancestor, because differences accumulate through mutation after lineages split. Technological developments — rapid DNA sequencing, comparative biochemistry and bioinformatics (computer analysis of large sequence databases) — have made it possible to compare whole genomes and have identified further evidence of evolutionary relationships.
Q6: How do comparative studies of proteins provide evidence for evolution?
Proteins are coded for by genes, so differences in a protein’s amino acid sequence reflect differences in the DNA. Comparing the amino acid sequence of the same protein in different species shows how related they are: the fewer amino acid differences, the more closely related the species. Proteins found in nearly all organisms, such as cytochrome c (used in cellular respiration), are useful for comparing distantly related groups.
Q7: What does a phylogenetic tree show, and how is it constructed?
A phylogenetic tree is a branching diagram showing evolutionary relationships between groups. Each branch point (node) represents a common ancestor; the tips are the groups being compared. Groups that share a more recent common ancestor (a more recent node) are more closely related. Trees are constructed from protein (amino acid sequence), genomic (DNA sequence) and/or anatomical information — the more shared similarities, the closer together the groups are placed.
Q8: Why is mutation described as the ultimate source of genetic variation?
A mutation is a change in the DNA sequence. Mutations are the only process that creates new alleles; meiosis (crossing over and independent assortment) and fertilisation only reshuffle existing alleles into new combinations. Most mutations are neutral or harmful, but occasionally a new allele gives a selective advantage. Only mutations in gametes (or the cells that produce them) are passed to offspring and enter the gene pool.
Sample Quiz Questions
Q1: Life is thought to have existed on Earth for approximately 3.5 billion years.
Answer: TRUE
The syllabus describes life on Earth as having existed for approximately 3.5 billion years, changing and diversifying over that time. Early evidence includes fossil stromatolites built by cyanobacteria.
Q2: The fossil record provides a complete and unbroken history of all life on Earth.
Answer: FALSE
The fossil record is incomplete due to the rarity of fossilisation, destruction of fossils through geological processes, and bias toward organisms with hard body parts. It provides valuable but fragmentary evidence of evolutionary history.
Q3: Homologous structures have similar underlying anatomy but may serve different functions, indicating common ancestry.
Answer: TRUE
Homologous structures (e.g. human arm, whale flipper, bat wing) share a similar bone arrangement inherited from a common ancestor but have been modified for different functions through divergent evolution.
Q4: Analogous structures indicate that two species share a recent common ancestor.
Answer: FALSE
Analogous structures (e.g. bird wing and insect wing) have similar functions but different underlying anatomy. They result from convergent evolution — similar environmental pressures, not common ancestry.
Q5: Vertebrate embryos look completely different from one another at every stage of development.
Answer: FALSE
Early vertebrate embryos are very similar — for example, all have pharyngeal arches and a post-anal tail at some stage. These shared features suggest common ancestry even though they develop into different adult structures.
Why It Matters
Continuity of life on Earth explains how life has persisted, changed and diversified over about 3.5 billion years. It brings together the evidence for evolution — DNA and protein comparisons, fossils, anatomy and embryology — and the mechanisms that change gene pools: mutation, natural selection, genetic drift and gene flow. These ideas explain how new species arise through allopatric speciation, how selective breeding has shaped crops and livestock, and why small, isolated populations of Australian species such as the Tasmanian devil are at greater risk of extinction. The topic builds directly on the Heredity content of Unit 3 (DNA, meiosis, mutation and alleles) and gives you the tools to evaluate claims about conservation and the management of gene pools.
Key Concepts
Evidence for Evolution
Comparative genomics, comparative studies of proteins, the fossil record, and comparative anatomy and embryology each give independent evidence of common ancestry. Phylogenetic trees built from protein, genomic or anatomical data show evolutionary relationships.
Mutation and Natural Selection
Mutation introduces new alleles. Selection pressures give some phenotypes a selective advantage in survival and reproduction, so the alleles responsible increase in frequency in the gene pool.
Dynamic Gene Pools
Allele frequencies change through mutation, differing selection pressures, random genetic drift (including the founder effect) and changes in gene flow. Drift has its greatest effect in small populations.
Speciation, Selective Breeding and Extinction
Differing selection pressures in geographically isolated populations can lead to allopatric speciation; macro-evolution is accumulated micro-evolution. Selective breeding changes gene pools by human choice, and reduced genetic diversity increases extinction risk.
Common Mistakes to Avoid
- Treating natural selection as goal-directed — selection acts on existing variation; organisms do not change “in order to” survive. Write “individuals with the advantageous allele were more likely to survive and reproduce”, not “the species evolved to…”.
- Confusing homologous with analogous structures — homologous structures indicate common ancestry; analogous structures result from similar selection pressures acting on unrelated groups.
- Saying natural selection or meiosis creates new alleles — only mutation introduces new alleles; selection changes their frequencies and meiosis reshuffles them.
- Describing genetic drift as adaptive — drift is random and can remove beneficial alleles or fix harmful ones, especially in small populations.
Study Tips
- Make a table of the five lines of evidence (comparative genomics, proteins, fossils, comparative anatomy, embryology) with what each compares and one example.
- Practise reading and building phylogenetic trees from amino acid or DNA difference tables — always identify the most recent common ancestor first.
- Write out the natural selection chain (variation → selection pressure → advantage → reproduction → allele frequency change) and apply it to a new example each time.
- For each of the four causes of gene pool change, learn one example and whether it increases or decreases the difference between populations.
- Draw a flow diagram of allopatric speciation from geographic isolation to reproductive isolation.
- Work through the practice questions in this set at least twice using spaced repetition — testing yourself repeatedly is the most effective revision strategy for long-term retention.
Related Topics
Exam Prep & Study Notes
Frequently Asked Questions
What does this WACE Biology Unit 3 topic cover?
It covers the Continuity of life on Earth content of Unit 3: life on Earth over about 3.5 billion years, the evidence for evolution (comparative genomics, protein comparisons, fossils, comparative anatomy and embryology), phylogenetic trees, mutation, natural selection, changes in gene pools through mutation, selection, genetic drift and gene flow, allopatric speciation, selective breeding and the extinction risk faced by populations with low genetic diversity.
What are the four conditions required for natural selection?
Natural selection requires variation in a trait, a genetic (heritable) basis for that variation, more offspring than the environment can support, and a selection pressure that gives some phenotypes better survival and reproduction. Over generations this changes allele frequencies in the gene pool.
Are these flashcards aligned to the SCSA WACE syllabus?
Yes. The cards follow the Continuity of life on Earth dot points of the SCSA Biology ATAR Year 12 syllabus, Unit 3 Continuity of species. Year 12 Biology is assessed through school-based assessment and the ATAR course examination, which samples content from Units 3 and 4.
Last updated: 9 October 2026 · 20 sample flashcards · 20 sample quiz questions · Content aligned to the SCSA Curriculum