How do humans breed plants and animals to have useful features?
How selective breeding chooses parents with desired characteristics over many generations, examples in crops and farm animals, and the benefits and risks including reduced variation and inbreeding.
A focused CCEA GCSE Biology answer on selective breeding, covering how parents with desired features are chosen over many generations, examples in crops and animals, and the benefits and risks including reduced variation.
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What this dot point is asking
CCEA wants you to describe how selective breeding chooses parents with desired characteristics over many generations, give examples in crops and farm animals, and explain the benefits and risks including reduced variation and inbreeding.
What selective breeding is
How it is done
The process is a repeated cycle: choose the parents with the desired characteristic, breed them, then from the offspring choose those with the feature and breed them again. Over many generations the alleles for the useful feature become more common, so the whole population improves.
Examples
Benefits and risks
The benefit is more useful organisms: more food, better resistance to disease, or desired traits. The risks are that selective breeding reduces variation (only chosen individuals breed), which can leave a population vulnerable to a new disease, and that inbreeding (breeding close relatives) can bring harmful recessive alleles together, causing health problems.
Examples in context
Example 1. Why pedigree dogs can have health problems. Many pedigree dog breeds have been selectively bred for a particular look, such as a flat face or a long back. Because breeders repeatedly mate closely related dogs to keep the look pure, harmful recessive alleles can pair up, causing inherited health problems such as breathing difficulties or hip disease. This is a clear, real example of the risks of selective breeding and inbreeding, and CCEA may ask you to discuss the downsides as well as the benefits.
Example 2. Comparing artificial and natural selection. Selective breeding and natural selection both make useful alleles more common over generations, but the selecting agent is different. In natural selection the environment decides which individuals survive and breed; in selective breeding humans decide which individuals breed. Seeing this parallel helps you understand both processes: in each case, the individuals that reproduce pass on their alleles, so the population gradually changes. CCEA often expects you to compare the two.
Try this
Q1. What is selective breeding? [2 marks]
- Cue. Humans choosing organisms with useful characteristics to breed, repeated over many generations.
Q2. Give one risk of selective breeding. [1 mark]
- Cue. It reduces variation (leaving the population vulnerable to disease), or it can cause inbreeding problems.
Exam-style practice questions
Practice questions written in the style of CCEA exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
CCEA 20205 marksDescribe how a farmer could use selective breeding to produce cattle that give more milk.Show worked answer →
Five marks for the repeated cycle of choosing and breeding.
The farmer chooses the cattle that produce the most milk (the desired characteristic) as parents.
These selected parents are bred together.
From the offspring, the farmer again chooses those that produce the most milk.
These are bred together, and the process is repeated over many generations.
Over time the average milk yield of the herd increases, because the alleles for high milk yield become more common.
Markers reward choosing the best parents, breeding them, selecting the best offspring, repeating over many generations, and the gradual improvement.
CCEA 20183 marksExplain one risk of selective breeding.Show worked answer →
Three marks for a risk explained clearly.
Selective breeding reduces variation, because only individuals with the chosen feature are bred, so the population becomes more genetically similar.
This is risky because if a new disease appears, the whole population may be vulnerable, as there is little variation to give resistance.
Repeated breeding of close relatives (inbreeding) can also increase the chance of harmful recessive alleles pairing up, causing health problems.
Markers reward reduced variation, vulnerability to disease or inbreeding problems, with a clear explanation.
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Sources & how we know this
- CCEA GCSE Biology specification — CCEA (2017)