Selective breeding (AQA GCSE Biology): Revision Notes
Selective breeding
What is selective breeding?
Selective breeding is also known as artificial selection. This is when humans choose which plants or animals to breed together. We do this to get offspring with the characteristics we want.
Farmers and breeders have been using this method for thousands of years. The process takes many generations to work properly - not just one.
The key to successful selective breeding is patience - it's a long-term process that requires consistent selection over multiple generations to see significant results.
The selective breeding process
Selective breeding follows these carefully planned steps:
- Choose the best individuals - Pick plants or animals that have the features you want from a large group
- Breed them together - Let these chosen individuals reproduce
- Select the best offspring - From the babies, choose the ones with the desired characteristics
- Repeat the process - Keep doing this over many generations until most offspring show the wanted features
This cycle continues until nearly all the offspring have the characteristics you're looking for. The success of selective breeding depends on consistently applying these steps across multiple generations.
Why do we use selective breeding?
Humans use selective breeding to create significant improvements in various areas:
- Animals that produce more food - cows that give more milk, chickens that lay more eggs
- Crops that resist disease - plants that don't get sick easily
- Pets with good behaviour - dogs that are gentle and friendly
- Plants with better appearance - flowers that are bigger or more colourful
Selective breeding has been crucial in developing most of the food we eat today. Almost all crops and livestock have been improved through this process over centuries.
Example: breeding high-milk-yield cattle
Worked Example: Developing High-Milk-Yield Cattle
A farmer wanting cows that produce lots of milk would follow this systematic approach:
Step 1: Choose a cow that produces plenty of milk
Step 2: Choose a bull whose mother also produced lots of milk
Step 3: Breed these two animals together
Step 4: From their babies, pick the female calves that produce the most milk when they grow up
Step 5: Breed these again with bulls from high-milk-producing mothers
Step 6: Continue this process for many generations
Result: Over time, most of the cattle will be high milk producers through this selective process.
Benefits and problems
Selective breeding brings both significant advantages and potential concerns:
Benefits:
- Animals produce more food (milk, meat, eggs)
- Crops grow better and resist diseases
- We get the specific characteristics we want
Problems:
- Inbreeding - When close relatives breed together, it can cause health problems
- Some breeds become more likely to get diseases or inherit defects
- Animal welfare issues - For example, cows producing so much milk they develop leg problems
Common Pitfall: Focusing only on one desired trait can accidentally reduce genetic diversity and create unexpected health problems. It's important to monitor the overall health and wellbeing of selectively bred organisms.
Summary
Key Points to Remember:
- Selective breeding means choosing which plants/animals breed together to get desired characteristics
- The process takes many generations to work - not just one
- We select the best individuals, breed them, then select the best offspring and repeat
- It can produce useful improvements but may cause health problems through inbreeding
- It's been used by humans for thousands of years to improve food production and other traits