Selective Breeding (AQA GCSE Biology): Revision Note

Impact of selective breeding

• Selective breeding involves selecting individuals with desirable characteristics and breeding them together

• Humans have been doing this for thousands of years, since they first bred food crops from wild plants and domesticated animals

Artificial selection

• Selective breeding, or artificial selection, is the process by which humans breed plants and animals for particular genetic characteristics

Selective breeding of animals

• Individuals with desired characteristics are bred together

• Offspring that show the desired characteristics are selected and bred together

• This process is repeated for many successive generations until there is a ‘new breed’ which will reliably show those selected characteristics in all offspring

• Animals are commonly selectively bred for various characteristics, including:

  • cows, goats and sheep that produce lots of milk or meat

  • chickens that lay large eggs

  • domestic dogs that have a gentle nature

  • sheep with good quality wool

  • horses with fine features and a very fast pace

Use this image

Selective breeding of plants

• Selective breeding of plants takes place in the same way as selective breeding of animals

• Plants are selectively bred by humans for development of many characteristics, including:

  • disease resistance in food crops

  • increased crop yield

  • hardiness to weather conditions (e.g. drought tolerance)

  • better tasting fruits

  • large or unusual flowers

Use this image

Problems with selective breeding

• Selective breeding can lead to inbreeding

• This occurs when closely related, genetically similar, organisms are bred together

• This results in a reduction in the number of alleles present in a population

• Inbred populations have reduced genetic variation, so there is an increased likelihood of:

  • organisms inheriting harmful genetic defects

  • organisms being vulnerable to new diseases (there is less chance of resistant alleles being present in the reduced gene pool)