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 introduces variation. Therefore, not al 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, Brassica oleracea was selectively bred to produce varieties like cauliflower, Brussels sprouts, kohlrabi, kale, cabbage and broccoli.

Desired Traits in Animals

Humans have selectively bred animals for various 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 resulted in many breeds of domestic dogs, each with distinct characteristics. Humans have bred and domesticated dogs to favour traits like intelligence and size, which are useful for tasks such as hunting. Domestic dogs descended from wolves.

Risks of Selective Breeding

When closely related animals and plants are bred together for favoUrable characteristics, the gene pool shrinks, leading to fewer alleles (different forms of a gene) in the population.

The smaller gene pool leads to inbreeding, which makes the population more prone to diseases. There is a lower chance that disease-resistant alleles will be present in the reduced gene pool.

Selectively breeding can also unintentionally reproduce characteristics that are harmful to an animal’s health. For example, pugs have squashed noses, which restricts their nasal passages and windpipes. This trait can make many pugs experience difficulty in breathing, similar to a sensation of suffocation.

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