Selective Breeding

Selective breeding, otherwise known as artificial selection, is the selection and breeding of animals and plants with desirable characteristics. For thousands of years, humans have bred food crops from wild plants, and domesticated animals.

The main steps in the selective breeding of animals and plants are:

1. Choose the desirable characteristic you want the new generation of animals or plants to have.

2. From a mixed population, pick the animals or plants that display these qualities.

3. Breed the animals or plants that you have selected.

  • Sexual reproduction causes variation. So, not all of the offspring will have the desired characteristic.

4. Select the best offspring who have the desired characteristics to produce the next generation.

5. Repeat this process for several generations until all of the offspring have the desired traits.

Desired Traits in Plants

Humans selectively breed plants for a variety of traits, including:

  • Increased crop yield
  • Resistance to diseases
  • Producing higher quality fruits
  • Ability to cope with extreme weather
  • Particular flower shapes and sizes

For example, the brassica oleracea was selectively bred to produce cauliflower, brussels sprouts, kohlrabi, kale, cabbage and broccoli.

Desired traits in Animals

Humans selectively breed animals for different characteristics. For example:

  • Animals that produce a lot of milk or meat
  • Chickens that lay large eggs
  • Sheep with high-quality wool

Selective breeding has led to many different breeds of the domestic dog, with many different characteristics. Humans bred and domesticated dogs to favour traits, such as intelligence and size, which are useful for hunting. The domestic dog descended from wolves.

Risks of Selective Breeding

Animals and plants that are closely related are bred together for favourable characteristics. As a result, the gene pool shrinks, resulting in fewer alleles (different forms of a gene) in a population.

The smaller gene pool causes inbreeding, which makes the animal more prone to disease. There is a lower chance that disease-resistant alleles will be present in the reduced gene pool. This means that more disease-carrying microorganisms will be in the gene pool.

When selectively breeding, it is also possible to unintentionally reproduce characteristics that are harmful to the animal’s health. For example, pugs have squashed noses, which restricts their noses and windpipes. This means that many pugs experience a constant sensation of suffocation.