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Selective breeding or artificial selection is when humans breed plants and animals for particular genetic characteristics. Humans have bred food crops from wild plants and domesticated animals for thousands of years.

Main steps in selective breeding

Selective breeding takes place over many generations. These are the main steps for both plants and animals:

1. Decide which characteristics are important enough to select.
2. Choose parents that show these characteristics from a mixed population. They are bred together.
3. Choose the best offspring with the desired characteristics to produce the next generation.
4. Repeat the process continuously over many generations, until all offspring show the desired characteristics.

Farmers selectively breed different types of cows with highly desirable characteristics in order to produce the best meat and dairy. Characteristics can be chosen for usefulness or appearance.

Desired characteristics in plants:

• disease resistance in food crops
• wheat plants that produce lots of grain
• large or unusual flowers

Desired characteristics in animals:

• animals that produce lots of milk or meat
• chickens that lay large eggs
• domestic dogs that have a gentle nature

The new varieties may be economically important. For example, they may provide more or better quality food, or allow farmers to feed more people.

Problems with selective breeding

Because of selective breeding, future generations of selectively bred plants and animals will all share very similar genes which will reduce variation. Genes and their different alleles within a population are known as its gene pool. Inbreeding can lead to a reduced gene pool, making it more difficult to produce new varieties in the future. This also makes organisms prone to certain diseases or inherited defects.

Benefits of selective breeding include:

• new varieties may be economically important, by producing more or better quality food
• animals can be selected that cannot cause harm, for example cattle without horns

Risks of selective breeding include:

• reduced genetic variation can lead to attack by specific insects or disease, which could be extremely destructive
• rare disease genes can be unknowingly selected as part of a positive trait, leading to problems with specific organisms, eg a high percentage of Dalmatian dogs are deaf
• creation of physical problems in specific organisms, eg large dogs can have faulty hips due to not being formed correctly