Selective breeding
Laura Armstrong & Joe Wolfensohn
Teachers
Recall Questions
This topic requires prior knowledge of variation and natural selection.
What causes genetic variation in a population?
Variation is caused by mutations and differences in alleles.
What is natural selection?
Natural selection is the process where the best-adapted organisms survive and reproduce.
How does a mutation lead to evolution?
If a mutation gives an advantage, it may increase survival chances, be passed on to offspring and spread through the population.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains selective breeding, then read the study notes. Once you’ve gone through them, don’t forget to try the practice questions!
What Is Selective Breeding?
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Selective breeding (also called artificial selection) is when humans choose organisms with desirable traits and breed them to produce offspring with those traits.
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This has been done for thousands of years with crops and animals.
Step-by-Step: How Selective Breeding Works
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Choose parents that show the desired characteristic (e.g. high milk yield).
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Breed them together.
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From the offspring, choose those that best show the desired trait.
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Breed the best offspring again.
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Repeat over many generations until the desired characteristic is common in all offspring.
Examples of Selective Breeding
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Cows bred for higher milk production.
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Farmers select cows with the highest milk yield and breed them.
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Plants bred for disease resistance
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Crops like wheat can be bred to resist certain fungi or viruses.
Examples of Other Desirable Traits
In Animals:
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More meat or milk (e.g. cows, sheep).
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Gentle behaviour (e.g. dogs).
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Fast growth rate.
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Resistance to disease.
In Plants:
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Disease resistance.
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Pest resistance.
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Higher yield (more fruit or grain).
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Drought tolerance.
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Large or colourful flowers.
Benefits and Risks
Benefits:
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Higher yields of food.
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Better quality produce (e.g. tastier fruit).
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Disease-resistant plants or animals.
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More docile pets and working animals.
Risks:
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Inbreeding: Reduces genetic diversity, increasing the chance of inherited diseases and health problems.
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Less resistant to new diseases or environmental changes.
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Ethical concerns over animal welfare and limiting natural variation.
Key Terms
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Selective breeding – Choosing parents to breed for specific traits.
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Desirable characteristic – A useful or attractive trait.
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Inbreeding – Breeding closely related individuals, often leading to health problems.
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Exam Tip
Make sure to clearly state the steps in selective breeding, including that it must be repeated over many generations.
Remember only cows (females) produce milk, never talk about a bull (male) producing a high milk yield!
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Practice Questions
Question 1
Many people have breathing problems because they are allergic to cats.
The allergy is caused by a chemical called Fel D1.
Different cats produce different amounts of Fel D1.
A cat has been bred so that it does not produce Fel D1.
The cat does not cause allergic reactions in humans.
Explain how the cat has been produced using selective breeding. (5 marks)
- parents who produce the least Fel D1 are selected.
- the parents are bred together to produce offspring.
- offspring who produce the least Fel D1 are selected and bred.
- this is repeated over many generations.
- over time the population of (selectively bred) cats will produce less Fel D1.
Question 2
Selective breeding could cause problems of inbreeding in cats.
Describe one problem inbreeding causes. (1 mark)
Cats are more likely to pass on genetic disorders or more likely to be susceptible to diseases/ have health problems.
More Practice
Try to answer these practice questions from the TikTok videos on your own, then watch the videos to see how well you did!