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Variation, selection and species

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Which difference most directly supplies heritable variation for selection?

  1. One adult loses a limb in an accident.
  2. Individuals carry different alleles that affect survival and can pass to offspring.
  3. Individuals that use a body part more develop it further and pass that change to offspring.
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Individuals carry different alleles that affect survival and can pass to offspring.

This connects variation to both reproductive success and inheritance.

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Which sentence completes a natural-selection explanation?

  1. The pressure produced the same useful mutation in every exposed individual.
  2. Each exposed individual changed colour during its lifetime and passed the new colour to its offspring.
  3. Individuals with the inherited advantage left more offspring carrying the relevant alleles.
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Individuals with the inherited advantage left more offspring carrying the relevant alleles.

Differential reproduction and inheritance connect the pressure to evolutionary change.

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Before an antibiotic was used, 1 in 1,000 bacteria in a population were resistant. After one week of use, 900 in 1,000 were resistant. Which conclusion is best supported?

  1. Each bacterium learned to resist the antibiotic.
  2. The antibiotic selected the resistant bacteria already present.
  3. The resistant bacteria became common by chance, not because of the antibiotic.
  4. The antibiotic caused the bacteria to mutate so that they resisted it.
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The antibiotic selected the resistant bacteria already present.

Resistant bacteria existed before use; they survived and multiplied while susceptible ones were killed.

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What additional observation most directly supports selection as the cause of a frequency rise?

  1. The frequency rose after immigration, but reproductive success was not measured.
  2. Carriers of the inherited variant consistently leave more offspring under the measured pressure.
  3. The final generation was measured on its own, without a comparison population or earlier sample.
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Carriers of the inherited variant consistently leave more offspring under the measured pressure.

This supplies the differential-reproduction link.

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Why can selection against aa fail to remove a completely?

  1. Aa individuals can transmit a without expressing the recessive harmful phenotype.
  2. Dominant alleles prevent recessive alleles from entering gametes.
  3. Selection acts against Aa carriers as strongly as against aa individuals, so both groups are removed at once.
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Aa individuals can transmit a without expressing the recessive harmful phenotype.

The allele can persist in carriers.

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Which evidence best supports a boundary under the biological species concept?

  1. Two populations live on opposite sides of a road.
  2. They are reproductively isolated and do not exchange genes through fertile offspring under natural conditions.
  3. Two populations look different and have different numbers of spots, so they must be separate species.
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They are reproductively isolated and do not exchange genes through fertile offspring under natural conditions.

This addresses the reproductive criterion.

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Which is NOT a problem in applying the biological species concept?

  1. Animals that interbreed in the wild
  2. Populations that live apart and never meet in nature
  3. Organisms that reproduce asexually
  4. Organisms known only from fossils
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Animals that interbreed in the wild

Interbreeding wild populations are exactly what the concept is designed for.

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Write a short answer, then compare it with a sample and check for missing ideas.

Question 1 of 7

Separate allele creation and reshuffling

4 marks

Explain how mutation, meiosis and sexual reproduction supply variation and why heritable variation is necessary for natural selection to cause evolutionary change. [4]

Do not say that every new combination is a new allele.

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