Selective Breeding
Build confidence in Selective Breeding for GCSE Biology with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. In selective breeding, humans choose organisms with desired characteristics to breed together, though this can reduce the gene pool.
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Topic overview
Selective breeding, also called artificial selection, is the process by which humans breed plants and animals for particular genetic characteristics.
Humans have been doing this for thousands of years, since first breeding food crops from wild plants and domesticating animals. The method is the same each time: choose parents with the desired characteristic, breed them, choose the offspring showing the characteristic most strongly, and repeat over many generations.
The drawback is inbreeding. Because the breeding population is small and closely related, there is reduced variation, so the population is more prone to disease and to inherited defects. This is a required evaluation point rather than an optional extra.
Revision notes
The method
Choose parents with the desired characteristic from a mixed population.
Breed them together. From the offspring, choose those showing the desired characteristic most strongly, and breed them. Repeat over many generations until all the offspring show the characteristic.
What is bred for
Disease resistance in food crops. Animals that produce more meat or milk.
Domestic dogs with a gentle nature. Large or unusual flowers. The characteristic must already exist as variation in the population before it can be selected for.
The problem of inbreeding
Repeatedly breeding closely related individuals reduces genetic variation in the population.
This makes the population more prone to disease, because a single pathogen may affect all of them, and increases the chance of inherited defects appearing.
Key points
- Selective breeding chooses parents with desired characteristics.
- It is also called artificial selection.
- The process is repeated over many generations.
- Uses include disease resistance and higher yields.
- Inbreeding reduces genetic variation.
- Reduced variation increases susceptibility to disease.
Worked examples
Example 1
Describe the process of selective breeding. [3 marks]
Model answer
Parents with the desired characteristic are chosen from a mixed population and bred together (1 mark). From the offspring, those showing the desired characteristic most strongly are selected and bred (1 mark). This is repeated over many generations until all the offspring show the characteristic (1 mark).
Example 2
Explain one disadvantage of selective breeding. [2 marks]
Model answer
It reduces the genetic variation in the population because closely related individuals are bred together (1 mark), which makes the population more prone to disease or to inherited defects (1 mark).
Example 3
Give two characteristics for which food crops might be selectively bred. [2 marks]
Model answer
Disease resistance (1 mark) and a larger yield of food (1 mark).
Common mistakes
Confusing selective breeding with genetic engineering.
Selective breeding chooses existing parents; genetic engineering transfers genes directly.
Forgetting that the process takes many generations.
It is gradual, unlike genetic engineering which is immediate.
Giving no disadvantage when asked to evaluate.
Inbreeding and reduced variation are the standard answers.
Saying selective breeding creates new characteristics.
It selects characteristics that already exist as variation in the population.
Exam tips
- Describe the process as a repeated cycle over generations.
- Always mention reduced variation as the drawback.
- Distinguish selective breeding from genetic engineering.
- Give specific examples of characteristics bred for.
Key terms
- Selective breeding
- Breeding organisms for particular genetic characteristics.
- Artificial selection
- Another name for selective breeding.
- Inbreeding
- Breeding closely related individuals, reducing variation.
- Yield
- The amount of useful product obtained.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.