Selective Breeding » Desired Characteristics

What you'll learn this session

Study time: 30 minutes

What selective breeding is and why it's important
How to identify desired characteristics in plants and animals
The process of selective breeding
Real-world examples of selective breeding
Advantages and disadvantages of selective breeding
Ethical considerations in selective breeding

Introduction to Selective Breeding

Humans have been changing plants and animals for thousands of years! Long before we knew about genes or DNA, farmers and breeders were selecting the best animals and plants to produce the next generation. This process is called selective breeding and it's one of the oldest forms of genetic modification.

Key Definitions:

Selective breeding: The process by which humans breed plants and animals for particular genetic traits.
Desired characteristics: Specific traits or features that are considered valuable or beneficial.
Artificial selection: Another term for selective breeding, where humans select which organisms breed based on desired traits.

🌱 Plants vs Animals

Plants: Desired traits might include higher yield, disease resistance, better taste, or specific appearance.

Animals: Desired traits often include more meat, more milk production, specific behaviours, or appearance features.

🔬 How It Works

Selective breeding works because of natural variation within species. By choosing which individuals get to reproduce, we can increase the frequency of desired traits in future generations.

The Process of Selective Breeding

Selective breeding follows a specific process to develop plants and animals with desired characteristics. Here's how it works:

Identify the desired characteristic - Decide what trait you want to enhance
Select parents - Choose individuals that show this trait strongly
Breed selected parents - Allow only these individuals to reproduce
Select offspring - Choose offspring that best show the desired trait
Repeat the process - Continue breeding selected offspring over many generations

Did You Know? 💡

All dog breeds - from tiny Chihuahuas to massive Great Danes - were developed from wolves through selective breeding! This shows how powerful selective breeding can be in creating variety within a species.

Desired Characteristics in Plants

Plant breeders select for many different traits depending on the purpose of the plant. Here are some common desired characteristics:

🌾 Crop Yield

Plants that produce more food per plant

Example: Modern wheat produces 3x more grain than ancient varieties

🦠 Disease Resistance

Plants that can fight off pests and diseases

Example: Blight-resistant potatoes developed after the Irish Potato Famine

🍋 Food Quality

Better taste, appearance, or nutritional value

Example: Sweet, juicy apples vs bitter wild apples

Desired Characteristics in Animals

Animal breeders select for different traits depending on the purpose of the animal. Here are some common desired characteristics:

🐄 Livestock Production

More meat, milk, or eggs

Example: Modern dairy cows produce 10x more milk than their wild ancestors

🐕 Companion Animals

Specific appearance or behaviour

Example: Dogs bred for herding, hunting, or as pets

🐤 Growth Rate

Animals that grow faster using less food

Example: Broiler chickens reach market weight in just 6 weeks

Case Study: The Development of Modern Wheat

One of the most important examples of selective breeding is the development of modern wheat varieties. Wild wheat had several problems:

Seeds would scatter easily (making harvesting difficult)
Low yield per plant
Small grain size

Through thousands of years of selective breeding, farmers developed wheat varieties with:

Seeds that stay on the plant until harvest
Much higher yield per plant
Larger grains with more nutritional content
Disease resistance

This selective breeding has been crucial for feeding the growing human population. Modern wheat varieties can produce up to three times more grain per plant than ancient varieties!

Case Study Focus: The Bulldog Problem

Not all selective breeding has positive outcomes. English Bulldogs have been bred for their flat faces and wrinkled skin, but these traits cause serious health problems. Many bulldogs suffer from breathing difficulties, overheating, skin infections and birthing problems. This shows how selecting for appearance without considering health can lead to welfare issues. This is an important ethical consideration in selective breeding.

Advantages and Disadvantages of Selective Breeding

👍 Advantages

Increased food production to feed growing populations
Disease-resistant crops and livestock
Improved quality of food products
Adaptation to different environments
Does not involve direct genetic modification techniques

👎 Disadvantages

Reduced genetic diversity within species
Can lead to health problems in animals
Takes many generations to achieve results
May reduce ability to adapt to new diseases or climate change
Ethical concerns about animal welfare

The Science Behind Selective Breeding

Selective breeding works because of several key biological principles:

Variation: Natural differences exist between individuals in a population
Heritability: Many traits can be passed from parents to offspring
Selection: By choosing which individuals reproduce, we can change the frequency of traits
Inbreeding: Breeding related individuals can strengthen desired traits but may also increase harmful traits
Crossbreeding: Breeding unrelated individuals with desired traits can create offspring with combinations of beneficial characteristics

Important to Remember! ⚠

Selective breeding is different from genetic engineering. Selective breeding works with natural variation and reproduction, while genetic engineering directly changes an organism's DNA in a laboratory. Both are forms of artificial selection, but they work in different ways.

Ethical Considerations

When studying selective breeding, it's important to consider the ethical implications:

Is it right to breed animals that may suffer health problems for human benefit?
What are the risks of reducing genetic diversity in our food supply?
How do we balance the need for increased food production with animal welfare?
Should there be limits on how much we can change an organism through breeding?

These questions don't have simple answers, but they're important to consider as we study the science of selective breeding.

Summary

Selective breeding is a powerful technique that has shaped the plants and animals we rely on today. By understanding how to identify and select for desired characteristics, humans have dramatically changed species to better suit our needs. While this has brought many benefits, particularly in food production, it also comes with risks and ethical considerations that must be carefully weighed.

In your IGCSE exam, you should be able to:

Explain what selective breeding is and how it works
Describe examples of desired characteristics in plants and animals
Outline the process of selective breeding
Discuss the advantages and disadvantages of selective breeding

🧠 Test Your Knowledge!