Selective Breeding in Animals

Section 1 of 7The process

1

Decide which characteristic is wanted, for example high milk yield in cattle.

2

Choose parent animals that show this characteristic most strongly. Several unrelated parents are often chosen so that close relatives need not be bred together later.

3

Breed the chosen parents together.

4

From the offspring, select those that show the desired characteristic best and breed them together.

5

Repeat this selection over many generations until the characteristic is well established in the breed.

Section 2 of 7Examples of characteristics selected

Food production

• Food production Cattle, goats and sheep with high milk or meat yield, and hens that lay many large eggs.

Other products

• Other products Sheep with good quality wool.

Behaviour and performance

• Behaviour and performance Dogs with a gentle nature, and horses with a fine build and fast pace.

Dog breeds

• Dog breeds All dog breeds have descended from wolves, but humans have selected different features to produce very different breeds.

Section 3 of 7Natural selection compared with artificial selection

Feature	Natural selection	Artificial selection
What drives it	The environment, with no human involvement	Humans choose which animals breed
Features favoured	Those that help survival and reproduction	Those useful to humans, not always useful to the animal
Speed	Usually very slow	Generally faster, because only chosen individuals reproduce

Section 4 of 7Benefits and drawbacks of selective breeding

Benefits

• Benefits Farmers obtain animals that give more milk, meat or eggs, which increases food supply and income.
• Animals can also be selected for disease resistance, so that fewer need treatment.

Drawbacks

• Drawbacks Breeding from a small number of animals reduces the variety of alleles in the population, so a new disease could affect them all.
• Breeding closely related animals can increase inherited health problems, so breeders choose unrelated parents where they can.

Section 5 of 7Why repetition is essential

1Generation 1

• Generation 1 Parents with the best trait are bred and their offspring show a slight improvement.

2Next generations

• Next generations Again the best offspring are chosen, so the useful alleles become more common.

3New breed

• New breed After many generations the population reliably shows the trait.
  • A single round of breeding is not enough.

Section 6 of 7Key terms

Term	Meaning
Selective breeding	Choosing parents with desired features and breeding them over many generations.
Artificial selection	Another name for selective breeding, driven by human choice.
Breed	A group of animals of one species with a set of shared characteristics.
Yield	The amount of a product, such as milk, that an animal produces.
Natural selection	The process by which better-adapted organisms survive and reproduce more in their environment.

Section 7 of 7Exam technique

1

Describing only one round of breeding — the process must be repeated for many generations.

2

Saying selective breeding creates new alleles — it increases the frequency of existing ones.

3

Writing that natural selection is chosen by humans — only artificial selection is.

4

Forgetting that artificially selected features may not help the animal survive in the wild.