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SBI3U · Unit 2 test review

Evolution: Test Review

Everything for the Unit 2 test on one page: the key facts from all 5 lessons, the mistakes that cost the most marks, and a practice test that points you back to the lessons you need.

Key facts

The Theory of Evolution and Its Evidence

  • Evolution is descent with modification: species change over generations and share common ancestors.
  • Lamarck's inheritance of acquired characteristics was rejected because changes to body cells during life are not passed on in eggs and sperm.
  • Homologous structures (same origin, different function) show common ancestry; analogous structures (same function, different origin) do not.
  • Radiometric dating: after half-lives, the fraction of isotope remaining is ; carbon-14 has years.
  • Five independent lines of evidence support evolution: fossils, biogeography, comparative anatomy, embryology and molecular biology (DNA and proteins).

Natural Selection and Adaptation

  • Natural selection needs four conditions: variation, overproduction, selection (differential survival and reproduction) and inheritance.
  • Fitness = relative reproductive success, not strength or speed.
  • Individuals do not evolve; populations evolve as allele frequencies change over generations.
  • Batesian mimicry: harmless mimics harmful. Müllerian mimicry: harmful species resemble each other.
  • Resistance evolves because the antibiotic or pesticide kills susceptible individuals and leaves resistant variants that were already present to reproduce.
  • Artificial selection = humans choose which individuals breed; it follows the same logic as natural selection.

Mechanisms of Evolutionary Change

  • Evolution at the population level = a change in allele frequencies over generations.
  • Allele frequency of = ; all allele frequencies for one gene add to 1.
  • Mutation is the only source of new alleles; gene flow, drift, selection and non-random mating change the frequencies of existing alleles.
  • Genetic drift is random and has its greatest effect in small populations; the bottleneck and founder effects are special cases.
  • Sexual selection favours traits that increase mating success, through competition (intrasexual) or mate choice (intersexual).

Selective Breeding: Benefits and Trade-offs

  • Selective breeding (artificial selection) needs variation, inheritance and human-chosen reproduction; it changes allele frequencies just as natural selection does.
  • Inbreeding makes lines uniform but increases homozygosity for harmful recessive alleles, causing inbreeding depression.
  • Hybridization combines traits from two lines and often produces hybrid vigour.
  • Canadian examples: Marquis wheat (early ripening), canola bred from rapeseed (low erucic acid and glucosinolates), Holstein dairy cattle (milk yield).
  • Monocultures of genetically uniform crops, such as the clonal Gros Michel banana, can be wiped out by a single disease.
  • Seed banks preserve genetic diversity; breeding mixes genes within a species, while genetic modification inserts specific genes, possibly from other species.

Speciation and Extinction

  • Biological species concept: populations that interbreed in nature to produce fertile offspring and are reproductively isolated from other groups.
  • Prezygotic barriers (habitat, temporal, behavioural, mechanical, gametic) prevent zygote formation; postzygotic barriers (reduced hybrid viability, reduced hybrid fertility, hybrid breakdown) act after it.
  • Allopatric speciation requires a geographic barrier; sympatric speciation occurs without one, often by polyploidy in plants.
  • Adaptive radiation: one ancestor gives rise to many species filling different niches (e.g. Darwin's finches).
  • Canadian risk categories: extinct, extirpated, endangered, threatened, special concern.

Where marks get lost

  • Saying "it's just a theory" as though a scientific theory were a guess. A scientific theory is a well-tested explanation supported by a large body of evidence. (The Theory of Evolution and Its Evidence)
  • Using analogous structures such as bird and insect wings as evidence that two groups are closely related. Only homologous structures show common ancestry. (The Theory of Evolution and Its Evidence)
  • Describing a vestigial structure as "completely useless". Vestigial means reduced from its ancestral function; the human tailbone, for example, still anchors muscles. (The Theory of Evolution and Its Evidence)
  • Explaining adaptation the Lamarckian way ("the animal needed longer legs, so it grew them and passed them on"). Individuals do not evolve; populations change as inherited variants become more or less common. (The Theory of Evolution and Its Evidence)
  • Saying humans evolved from chimpanzees. Humans and chimpanzees share a common ancestor; neither species is the ancestor of the other. (The Theory of Evolution and Its Evidence)
  • Saying bacteria "become resistant because they get used to the antibiotic". Resistant variants already exist (or arise by random mutation); the antibiotic kills the others. (Natural Selection and Adaptation)
  • Treating fitness as physical strength. Fitness is reproductive success, so an organism that survives but never reproduces has a fitness of zero. (Natural Selection and Adaptation)
  • Saying an individual moth "evolved" a darker colour. Individuals keep their inherited traits; the population's proportion of dark moths changes. (Natural Selection and Adaptation)
  • Mixing up the two kinds of mimicry. In Batesian mimicry the mimic is harmless; in Müllerian mimicry all the look-alikes are harmful. (Natural Selection and Adaptation)
  • Thinking artificial selection creates brand-new traits. Breeders can only select from variation that already exists or that appears by chance mutation. (Natural Selection and Adaptation)
  • Using instead of as the denominator when calculating allele frequencies. Every diploid individual carries two copies of each gene. (Mechanisms of Evolutionary Change)
  • Thinking genetic drift makes populations better adapted. Drift is random and can even remove helpful alleles, especially in small populations. (Mechanisms of Evolutionary Change)
  • Believing a population that recovers in numbers after a bottleneck also recovers its genetic diversity. Lost alleles only return through new mutation or gene flow. (Mechanisms of Evolutionary Change)
  • Confusing the founder and bottleneck effects. Founder effect: a small group leaves to start a new population. Bottleneck: the original population itself is drastically reduced. (Mechanisms of Evolutionary Change)
  • Saying mutations happen when an organism needs a new trait. Mutations are random with respect to need; selection acts afterwards. (Mechanisms of Evolutionary Change)
  • Thinking selective breeding creates new genes. It only reshuffles and concentrates alleles that already exist; new alleles come from mutation. (Selective Breeding: Benefits and Trade-offs)
  • Treating selective breeding and genetic modification as the same thing. Breeding crosses related organisms over many generations; GM inserts specific genes, sometimes from unrelated species. (Selective Breeding: Benefits and Trade-offs)
  • Assuming inbreeding causes mutations. Inbreeding does not create harmful alleles; it makes offspring more likely to inherit two copies of recessive alleles already present. (Selective Breeding: Benefits and Trade-offs)
  • Selecting parents based on traits caused by the environment, such as a well-fed animal's size. Only inherited differences respond to selection. (Selective Breeding: Benefits and Trade-offs)
  • Believing a high-yielding monoculture is always the safest choice. Uniformity means one new pest or disease can destroy the whole crop. (Selective Breeding: Benefits and Trade-offs)
  • Saying two animals are the same species simply because they can mate. Under the biological species concept the offspring must also be fertile; horses and donkeys are separate species. (Speciation and Extinction)
  • Mixing up prezygotic and postzygotic. The dividing line is the zygote: barriers that stop mating or fertilization are prezygotic; problems with the hybrid itself are postzygotic. (Speciation and Extinction)
  • Thinking sympatric speciation needs a physical barrier. Allopatric speciation has a geographic barrier; sympatric speciation happens in the same place. (Speciation and Extinction)
  • Confusing extinct with extirpated. An extirpated species is gone from the wild in one region (such as Canada) but still survives somewhere else. (Speciation and Extinction)
  • Believing Darwin's finches each changed their beaks to suit their food. The ancestral population varied, and different islands and food sources selected for different inherited beak shapes over many generations. (Speciation and Extinction)

Practice test

25 questions from across the unit. Each one shows the lesson it comes from.

  1. The Theory of Evolution and Its Evidence
    1
    Which idea from Charles Lyell was most important to Darwin's thinking?
  2. The Theory of Evolution and Its Evidence
    2
    A piece of charcoal from an ancient campfire contains 25% of its original carbon-14. The half-life of carbon-14 is 5730 years. How old is the charcoal, in years?
    years
  3. The Theory of Evolution and Its Evidence
    3
    Which pair is an example of analogous structures?
  4. The Theory of Evolution and Its Evidence
    4
    Put these events in order from longest ago to most recent.
    1. 1Darwin publishes On the Origin of Species (1859)
    2. 2Archaeopteryx lives (about 150 million years ago)
    3. 3Tiktaalik lives (about 375 million years ago)
    4. 4Earth forms (about 4.6 billion years ago)
    5. 5Single-celled life appears in the fossil record
  5. The Theory of Evolution and Its Evidence
    5
    Why is DNA comparison considered especially strong evidence for evolution?
  6. Natural Selection and Adaptation
    6
    In evolutionary biology, which individual has the highest fitness?
  7. Natural Selection and Adaptation
    7
    A population of 1 × 10⁹ bacteria contains resistant cells at a frequency of 1 in 1 × 10⁷. An antibiotic kills every non-resistant cell, and the survivors divide every 20 minutes. How many bacteria are present 2 hours after the treatment?
    bacteria
  8. Natural Selection and Adaptation
    8
    Put the steps of natural selection in order.
    1. 1The variant becomes more common over many generations
    2. 2Their offspring inherit the helpful variant
    3. 3Individuals with a helpful variant survive and reproduce more
    4. 4Individuals in a population vary in an inherited trait
    5. 5More offspring are produced than can survive
  9. Natural Selection and Adaptation
    9
    Which statement about antibiotic resistance is correct?
  10. Natural Selection and Adaptation
    10
    What type of mimicry involves two or more harmful species that resemble each other?
  11. Mechanisms of Evolutionary Change
    11
    A population of 200 mice has 90 BB, 80 Bb and 30 bb individuals. What is the frequency of allele B? Give your answer as a decimal to two places.
  12. Mechanisms of Evolutionary Change
    12
    A population of 400 frogs has a frequency of 0.30 for an allele. 100 frogs from another population, where the frequency is 0.80, join and interbreed. What is the new allele frequency? Give your answer to two decimal places.
  13. Mechanisms of Evolutionary Change
    13
    Why does genetic drift have a much stronger effect in small populations?
  14. Mechanisms of Evolutionary Change
    14
    Match each scenario to the mechanism of evolution it illustrates.
    A copying error in DNA creates a new allele
    Wolves migrate between two packs and breed
    A flood randomly kills most of a small beetle population
    Male moose with larger antlers win more contests for mates
    Related plants self-pollinate and produce more homozygous offspring
  15. Mechanisms of Evolutionary Change
    15
    A peahen chooses to mate with the peacock that has the largest, most colourful tail. This is an example of:
  16. Selective Breeding: Benefits and Trade-offs
    16
    Which condition must be true for selective breeding to change a population over generations?
  17. Selective Breeding: Benefits and Trade-offs
    17
    The cross that produced Marquis wheat was made in 1892, and the variety was released to farmers in about 1909. How many years did the breeding program take? Give a whole number.
  18. Selective Breeding: Benefits and Trade-offs
    18
    Put the steps of a selective breeding program in order.
    1. 1Repeat over many generations
    2. 2Measure the offspring and keep the best
    3. 3Cross the best individuals as parents
    4. 4Decide which trait to improve
    5. 5Collect individuals that vary in that trait
  19. Selective Breeding: Benefits and Trade-offs
    19
    Which of these is an example of genetic modification rather than selective breeding?
  20. Selective Breeding: Benefits and Trade-offs
    20
    How does inbreeding lead to more inherited disorders?
  21. Speciation and Extinction
    21
    According to the biological species concept, two organisms belong to the same species if they:
  22. Speciation and Extinction
    22
    A zebra species has a diploid number of 44 and a horse has 64. Assuming normal gametes from each parent, how many chromosomes would a zebra-horse hybrid have?
    chromosomes
  23. Speciation and Extinction
    23
    What type of speciation occurs when a geographic barrier divides a population?
  24. Speciation and Extinction
    24
    Match each isolating mechanism to its example.
    Temporal isolation
    Mechanical isolation
    Gametic isolation
    Habitat isolation
    Reduced hybrid fertility
  25. Speciation and Extinction
    25
    Which species is most likely to be vulnerable to extinction if its habitat changes rapidly?

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