Question 1
Paper 1A style
Which process generates new alleles?
- Mutation
- Crossing over
- Random orientation of bivalents
- Random fertilisation
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Answer: A [1]
Question 2
Paper 1A style
Which is a density-independent selection pressure?
- Competition for nesting sites
- A very cold winter
- Predation by owls
- Spread of disease in a crowded population
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Answer: B [1]
Question 3
Paper 2A style
A gardener grows a plant in rich, fertile soil and it grows very tall. Explain why its offspring will not inherit this extra height.
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- height was acquired due to an environmental factor / soil, not genes [1]
- acquired characteristics are not encoded in the base sequence of genes / DNA of gametes [1]
- so they cannot be passed on / only heritable traits can evolve [1]
- max 2
Question 4
Paper 1B style
In an experiment modelled on Endler's work, guppies were kept in replicate ponds with no predator, with the weak predator Rivulus, or with the strong predator Crenicichla. The table shows the mean number of coloured spots per male (practice data). (a) Calculate the percentage change in mean spots per male in the no-predator ponds from 0 to 14 months. [2] (b) Compare the results for Rivulus and Crenicichla ponds. [2] (c) Explain the trend in the Crenicichla ponds. [2]
| Treatment | 0 months | 5 months | 14 months |
|---|---|---|---|
| No predator | 10.0 | 11.2 | 12.5 |
| Rivulus | 10.0 | 11.0 | 12.2 |
| Crenicichla | 10.0 | 9.1 | 8.4 |
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- (a) (12.5 − 10.0) ÷ 10.0 × 100 [1]
- (a) +25% / increase of 25% [1]
- (b) Rivulus: spots increased (10.0 to 12.2) whereas Crenicichla: spots decreased (10.0 to 8.4) [1]
- (b) both start at the same value / both change in the same time / difference grows with time [1]
- (c) brightly coloured males are more conspicuous / more likely to be eaten by Crenicichla [1]
- (c) males with fewer spots survive and reproduce more, passing on alleles for fewer spots [1]
- (c) predation outweighs sexual selection / female preference for colourful males OWTTE [1]
- max 6
Question 5
Paper 2B style
Explain how natural selection can lead to evolutionary change in a population.
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- variation exists between individuals in a population [1]
- mutation generates new alleles [1]
- sexual reproduction / meiosis and fertilisation generate new combinations of alleles [1]
- more offspring are produced than the environment can support / overproduction [1]
- population exceeds carrying capacity so there is competition for limited resources, e.g. food [1]
- selection pressures, e.g. predation / extreme temperature, affect individuals differently [1]
- better-adapted individuals / those with higher fitness survive and reproduce more [1]
- they pass on alleles for the favourable traits to offspring [1]
- only heritable traits / not acquired characteristics are passed on [1]
- over many generations the frequency of the favourable trait / allele increases [1]
- max 6