A fish farmer wants to produce trout that grow faster and are more resistant to disease. Explain how the fish farmer could use selective breeding to achieve this over several generations.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Selective breeding (also called artificial selection) has been used for thousands of years to improve the characteristics of animals kept by humans. The fish farmer currently has a large population of trout with variation in growth rate and disease resistance.
Model answer (5 marks)
Select trout that grow fast and/or are disease resistant from the existing population.
Breed the selected trout together (allow them to mate or cross them).
From the offspring, choose those that show the desired traits.
Repeat this selection and breeding over many generations.
As the process continues, the alleles for fast growth and disease resistance become more common, so the population increasingly displays the desired characteristics.
Breed the selected trout together (allow them to mate or cross them).
From the offspring, choose those that show the desired traits.
Repeat this selection and breeding over many generations.
As the process continues, the alleles for fast growth and disease resistance become more common, so the population increasingly displays the desired characteristics.
Examiner tips
- Use the exact terms from the mark scheme: 'select', 'breed', 'select offspring', 'repeat', 'over time'
- Show the sequence of steps clearly and link each to the outcome of increased allele frequency
- Mention that the process is iterative and spans several generations
Common mistakes
- Confusing selective breeding with natural selection
- Failing to mention that the process is repeated over generations
- Using vague language like 'improve' instead of the specific traits
Mark scheme (5 marks)
- Select/identify trout with the desired characteristics (fast growth AND/OR disease resistance) from the population
- Breed the selected trout with each other (allow them to reproduce / cross the selected individuals)
- Select offspring that show the desired characteristics (fast growth and/or disease resistance) from the next generation
- Repeat the process over many generations
- Over time, the desired characteristics become more common / the alleles for the desired traits increase in frequency in the population
Key terms in this question
selective breeding · generation
Related
- All Pearson Edexcel A-Level Biology A (9BI0) revision notes →
- How to answer a "Explain" question →
- Decode the mark scheme abbreviations →
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