Selective breeding (AQA GCSE Biology Combined Science): Revision Notes
Selective breeding
What is selective breeding?
Selective breeding is a process where humans choose plants and animals with useful traits to breed together. This is also called artificial selection. People have used this method for thousands of years to create better crops and livestock.
The goal is to produce offspring that have particular characteristics we want. This might be cows that give more milk, crops that resist disease, or dogs with gentle personalities.
Selective breeding relies on the principle that useful traits can be passed from parents to offspring through genetics. By carefully choosing which individuals reproduce, humans can gradually change the characteristics of entire populations over time.
The selective breeding process
Selective breeding works through a simple cycle that happens over many generations. The process follows a systematic approach that must be repeated consistently to achieve the desired results.
The Selective Breeding Cycle
Step 1: Choose individuals with the desired characteristic from a mixed population
Step 2: Breed these selected individuals together
Step 3: Select the offspring that show the desired characteristic
Step 4: Repeat this process over many generations until all offspring have the desired trait
This process takes time because it happens over many generations, not just one. Each generation gets closer to having all the characteristics we want.
Examples of selective breeding
Cattle breeding for milk production
Farmers have successfully used selective breeding to dramatically improve milk production in dairy cattle. The process requires careful selection and patience over multiple generations.
Worked Example: Breeding High-Milk-Producing Cattle
Step 1: Choose a cow that produces lots of milk
Step 2: Breed this cow with a bull whose mother also gave lots of milk
Step 3: Select female offspring that produce high amounts of milk
Step 4: Breed these females with bulls from high-milk-producing mothers
Step 5: Repeat this process over many generations
Other characteristics that can be selected
People choose to breed for characteristics that are useful or attractive across many different species:
- Animals: More milk or meat production, gentle nature
- Food crops: Resistance to plant diseases
- Domestic dogs: Gentle temperament
- Plants: Large or unusual flowers
Results of selective breeding
Selective breeding has been remarkably successful in agriculture and animal husbandry. The evidence clearly demonstrates the power of this technique when applied consistently over time.
For example, milk production in cows more than doubled between 1957 and 2007. This helps farmers produce more milk from fewer cows, which reduces costs and improves efficiency.
The success of selective breeding programmes often exceeds what might be expected from natural selection alone, because humans can make breeding decisions based on specific goals rather than just survival and reproduction.
Problems with selective breeding
While selective breeding offers many benefits, it also creates significant challenges that must be carefully managed.
Inbreeding issues
When selective breeding involves close relatives, it can cause inbreeding. This happens when related animals breed together repeatedly.
Risks of Inbreeding:
- Inherited diseases
- Physical defects
- Weaker animals overall
Inbreeding occurs because the gene pool becomes smaller when only the "best" individuals are selected for breeding, making it more likely that related animals will mate.
Animal welfare concerns
Some selective breeding creates serious ethical problems that affect both animals and farmers:
Animal Welfare Issues:
- Animals may suffer from health issues due to extreme breeding for certain traits
- Cows bred for very high milk production can develop leg and udder problems
- This affects animal welfare and increases vet bills for farmers
The benefits of selective breeding must be weighed against these animal welfare concerns.
Key Points to Remember:
- Selective breeding is also called artificial selection
- The process takes many generations to work properly
- Humans select individuals with desired traits to breed together
- Examples include breeding cows for more milk and crops for disease resistance
- Inbreeding can cause health problems in animals
- There are ethical concerns about animal welfare that must be considered