🌱 Steps 1 and 2
1. Choose parents with the desired characteristic from a mixed population.
2. Breed these parents together.
Variation and Evolution » Selective Breeding
What you'll learn this session
Study time: 30 minutes
AQA spec: 4.6.2.3
- What selective breeding is and how humans use it
- The steps of selective breeding over many generations
- Useful and attractive characteristics that humans choose
- The benefits, risks and ethical issues, including inbreeding
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Unlock This CourseWhat is selective breeding?
In the last lesson, natural selection changed populations because the environment decided which individuals survived. In this lesson, humans make the choice instead.
Humans have done this for thousands of years. The first farmers took wild plants and bred them into food crops. They also kept wild animals and bred them into domesticated animals, such as cows and sheep.
Key terms:
- Selective breeding (artificial selection): the process by which humans breed plants and animals for particular genetic characteristics.
- Inbreeding: a problem that selective breeding can lead to, where some breeds are particularly prone to disease or inherited defects.
The word genetic matters. The characteristic being chosen must be passed on in the genes, or breeding will not make it more common.
How selective breeding works
The process always follows the same steps. It is slow, because it works over many generations.
🔄 Steps 3 and 4
3. From the offspring, choose those with the desired characteristic and breed them together.
4. Keep repeating this over many generations, until all the offspring show the desired characteristic.
Worked example
A farmer wants cows that give more milk. The farmer picks the cows that give the most milk and breeds them together. Of the calves, the ones that grow into the best milk producers are bred together. After many generations, the whole herd gives more milk than the original herd did.
What characteristics do humans choose?
Humans choose a characteristic because it is useful or because it looks good. Here are the examples to know.
🌾 Disease resistance in food crops
Crop plants that are not harmed by a disease give a bigger harvest. Farmers breed together the plants that resist the disease.
🥙 More meat or milk
Animals that produce more meat or more milk give farmers more food to sell. Those are the animals that get bred.
🐕 A gentle nature in dogs
Domestic dogs with a gentle nature are safer and easier to live with. Breeders choose gentle dogs as parents.
🌺 Large or unusual flowers
Some people choose flowers for their size or their unusual look. This is chosen for appearance, not for use.
Benefits, risks and ethical issues
You may be asked to explain the impact of selective breeding. Think about the good points, the bad points and the questions of right and wrong.
✅ Benefits
More food can be produced from the same land and the same number of animals. Crops can be protected from disease. Animals can be made easier and safer to handle.
⚠ Risks
Selective breeding can lead to inbreeding. Some breeds are then particularly prone to disease or inherited defects.
Inbreeding happens when breeders keep using a small number of closely related animals. The result is a breed that is particularly prone to disease or inherited defects.
Ethical issues
Ethics means questions about what is right and wrong. Is it right to breed animals that may suffer inherited defects, just so they look a certain way? Is it right to choose animals only for what is useful to humans? People have different opinions, so give both sides in an answer.
Common mistakes
1. Saying that animals choose to change. In selective breeding, humans do the choosing.
2. Saying it happens in one generation. It takes many generations.
3. Mixing it up with natural selection. In natural selection the environment decides who survives. In selective breeding, humans decide who breeds.
Exam-style question
A farmer has a field of wheat. Some of the wheat plants are resistant to a fungal disease. The farmer decides to use selective breeding.
(a) Describe how the farmer could use selective breeding to produce a crop in which all the plants are resistant to the disease. [3 marks]
(b) Suggest one benefit of this to the farmer. [1 mark]
(c) A breeder has used selective breeding for many generations on a breed of dog. Explain one problem that can result. [2 marks]
Model answer
(a) Choose the resistant plants as parents and breed them together (1). Select the offspring that are resistant and breed these together (1). Repeat for many generations until all the plants are resistant (1).
(b) The crop is not harmed by the disease, so the farmer gets a bigger harvest (1).
(c) Inbreeding can result (1). The breed is then more prone to disease or inherited defects (1).
Exam tip
In a "describe" question on selective breeding, show the repeating. Use the words "choose", "breed together", "offspring" and "many generations" to pick up the marks.