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The main problems with selective breeding are reduced genetic variation and inbreeding, which make organisms prone to disease or inherited defects. Free notes.
The Impact and Problems of Selective Breeding is part of Variation and evolution in GCSE Edexcel Higher Biology.
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GCSE Edexcel Higher
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The main problems with selective breeding are reduced genetic variation and inbreeding, which make organisms prone to disease or inherited defects. Free notes.
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Use this lesson to stay inside Variation and evolution while connecting the detail back to the wider Topic 4: Natural selection and genetic modification topic.
Read the core explanations from The Impact and Problems of Selective Breeding before testing yourself from memory.
Farmers have been shaping life for thousands of years. That tiny chihuahua and massive Great Dane? Both descended from wolves through selective breeding. Your breakfast cereal? Those wheat grains are three times larger than their wild ancestors. But this power comes with hidden costs that can threaten entire breeds.
Think of selective breeding as nature's editing tool in human hands. Instead of random mating, we choose the 'best' individuals as parents. The fastest horses breed with other fast horses. The juiciest tomatoes produce seeds for next year's crop.
Selective breeding has transformed our food supply and created remarkable animals. Modern dairy cows produce 6-7 times more milk than their ancestors. Wheat yields have tripled since the 1960s. Chickens grow to market weight in half the time they used to.
Food plants benefit enormously: Larger fruits and vegetables, disease resistance, longer shelf life, and crops that ripen at the same time for easier harvesting. Corn cobs have grown from thumb-sized to today's massive ears through centuries of selective breeding.
Domesticated animals show dramatic changes: Sheep produce more wool, pigs grow leaner meat, and dogs have been shaped into hundreds of breeds for specific jobs - from herding sheep to detecting explosives.
Here's where selective breeding gets dangerous. When we choose only the 'best' individuals to breed, we're actually throwing away genetic variation. It's like editing a book by removing most of the words - eventually, you can't tell the full story anymore.
Inbreeding happens when the gene pool becomes too small. If only a few 'champion' animals are used for breeding, their offspring become increasingly related. This is like photocopying a photocopy - each generation loses quality.
The consequences are serious: Purebred dogs suffer from hip dysplasia, breathing problems, and heart defects. Some chicken breeds grow so fast their legs can't support their weight. Certain pig breeds are so muscular they can't give birth naturally.
When genetic variation drops, entire populations become sitting ducks for disease. Think of it like a computer virus - if all computers run identical software, one virus can crash them all. But if they're all different, some will survive.
The Irish Potato Famine of the 1840s shows this danger. Irish farmers grew mainly one variety of potato. When a fungal disease struck, it wiped out the entire crop because all plants were genetically identical. Over one million people died.
Modern examples include: Banana plantations threatened by Panama disease, purebred dogs with compromised immune systems, and dairy cows susceptible to specific infections because they're so genetically similar.
Let's examine specific cases where selective breeding has both helped and harmed. These examples show up frequently in exams because they demonstrate the double-edged nature of artificial selection.
Worked example: Analysing a Selective Breeding Programme
A farmer wants to develop a new variety of wheat that is resistant to drought and produces large grains. Explain the process and potential problems. [6 marks]
Answer: Selective breeding can develop desired traits but risks creating genetic bottlenecks that make crops vulnerable to disease outbreaks.
Success story: Modern corn produces 6 times more grain per plant than its ancestor, teosinte. Selective breeding over 9,000 years transformed a grass with tiny seeds into today's massive corn cobs.
Problem case: Pug dogs have been bred for flat faces, but this causes breathing difficulties, eye problems, and overheating. The 'cute' appearance comes at the cost of the animal's health and quality of life.
Selective breeding questions often ask you to evaluate - that means discussing both benefits and problems. Don't just list advantages; examiners want to see you understand the trade-offs involved.
Command word focus: 'Evaluate the use of selective breeding' means discuss advantages AND disadvantages, then reach a conclusion about whether it's worthwhile overall. Don't just describe the process.
Common exam mistake: Students often forget to mention disease susceptibility when discussing problems. This is a key specification point - inbreeding makes organisms 'particularly prone to disease or inherited defects'.
Published by Revise Right. Use the official specification reference to check the requirements for your course. Content updated: 2026-03-23.
Move to the related lessons or back to the topic page when you need the wider sequence before exam-style practice.
Inbreeding is breeding between closely related organisms, which reduces genetic variation and can increase the risk of inherited defects and disease susceptibility. It happens when only a few champion animals are used for breeding, so their offspring become increasingly related.
Banana plantations are threatened by Panama disease because selective breeding has made the plants so genetically similar. When genetic variation drops, entire populations become vulnerable to a single disease.
A genetic bottleneck happens when genetic variation in a population drops so far that the whole population becomes vulnerable to disease. If all computers run identical software, one virus can crash them all, but in a varied population some individuals will survive.
The main problems with selective breeding are reduced genetic variation and inbreeding, which make organisms prone to disease or inherited defects. Purebred dogs suffer from hip dysplasia, breathing problems and heart defects, and some chicken breeds grow so fast their legs cannot support their weight.
Pugs have breathing problems because they have been selectively bred for flat faces. This bred-in appearance also causes eye problems and overheating, so the cute look comes at the cost of the animal's health and quality of life.
Purebred dogs suffer from hip dysplasia, breathing problems and heart defects because inbreeding reduces genetic variation. Some purebred dogs also have compromised immune systems, making them more prone to disease.
Selective breeding makes organisms more prone to disease because it reduces genetic variation, so if all individuals are genetically similar one disease can wipe them all out. In the Irish Potato Famine of the 1840s, a fungal disease wiped out a crop of genetically identical potatoes.
Selective breeding has transformed food production: modern dairy cows produce 6-7 times more milk than their ancestors, wheat yields have tripled since the 1960s, and modern corn produces 6 times more grain per plant than its ancestor, teosinte.
Modern dairy cows produce 6-7 times more milk than their ancestors because of selective breeding. Selective breeding has also tripled wheat yields since the 1960s and halved the time chickens take to grow to market weight.
The Irish Potato Famine of the 1840s shows the danger of low genetic variation. Farmers grew mainly one variety of potato, so when a fungal disease struck it wiped out the entire crop because all plants were genetically identical, and over one million people died.
Corn has changed from a grass with tiny seeds, teosinte, into today's massive corn cobs through selective breeding over 9,000 years. Modern corn produces 6 times more grain per plant than its ancestor.
Selective breeding has caused some chicken breeds to grow so fast their legs cannot support their weight. Certain pig breeds are so muscular they cannot give birth naturally.
A farmer would breed drought-resistant wheat by selecting plants that survive with less water and produce large grains, breeding them together, then choosing the best offspring and repeating over many generations. Reduced genetic variation could make the crop more vulnerable to disease.
The problems of inbreeding can be reduced by introducing new genetic material to maintain the health of a population. Breeding programmes need to balance desired traits with genetic diversity to avoid disease susceptibility and inherited defects.