Selective breeding

Pedigree dogs come in lots of different varieties. They may be different colours and sizes, but they are all still dogs. They are all still the same species. The different varieties of dog have been produced through deliberate selective breeding by dog-owners.

Five dogs lined up in a row from biggest to smallest
Five very different breeds of dog

These are the steps taken to select a particular feature in an organism:

  1. choose individuals with the desired feature
  2. let only these individuals reproduce
  3. choose the offspring that have the desired feature
  4. let only these individuals reproduce
  5. repeat steps 3 and 4 until you have produced a variety in which all the individuals show the desired feature

For example, suppose you wanted a variety of cow that produced a lot of milk. This is what you could do:

  1. select the cows in your herd that produce the most milk
  2. let only these cows reproduce
  3. select the offspring that produce the most milk
  4. let only these individuals reproduce
  5. keep repeating the process of selection and breeding until you produce a breed that consistently produces a lot of milk
Friesian cow grazing in a field
Friesian cows are a variety that produce a lot of milk

Other examples of selective breeding

The key to success is to identify the feature you want, only breed from the individuals that have that feature, and do not allow individuals with undesirable features to breed. Here are some examples of what selective breeding can produce:

  • hens that lay big eggs of a particular colour
  • cattle that produce lots of meat
  • tomato plants that produce lots of tomatoes
  • crops that are resistant to certain plant diseases
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