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GCSE Biology Revision

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GCSE Biology revision

Selective breeding

Variation and evolution

AQA 4.1.1.1
Your specification

AQA student objectives

Learning pathway

All · Most · Some

ALL 🎯

Identify and describe What is Selective Breeding?, Examples of Selective Breeding and How Does Selective Breeding Work? in the context of selective breeding.

MOST 🎯🎯

Explain the relationships between What is Selective Breeding?, Examples of Selective Breeding and How Does Selective Breeding Work? and how they contribute to selective breeding.

SOME 🎯🎯🎯

Apply and analyse knowledge of What is Selective Breeding?, Examples of Selective Breeding and How Does Selective Breeding Work? to interpret unfamiliar information about selective breeding.

Revision summary

Key knowledge

Read on screen, then print for Cornell-style active revision.

What is Selective Breeding?

  • Selective breeding is the process of choosing individuals with desirable characteristics from a population and breeding them together to produce offspring with even better traits
  • Humans have practised selective breeding for thousands of years, ever since the development of agriculture

Examples of Selective Breeding

  • Cows are selectively bred to produce greater quantities of meat or milk
  • Crops are selectively bred to be resistant to diseases, improving farm yields
  • Cats and dogs are selectively bred for friendly temperaments, making them suitable as pets
  • Plants are selectively bred to produce large or unusually shaped flowers for ornamental purposes

How Does Selective Breeding Work?

  • Breeders examine all individuals in their existing stock and identify those with the most desirable characteristics
  • The selected individuals are bred together to produce the next generation, which hopefully shows improved traits
  • This process is repeated over many generations, always selecting the best individuals to breed from each time
  • Over thousands of years of repeated selective breeding, dramatic changes can occur — for example, modern sweet corn looks vastly different from its wild ancestor found over
  • 10,000 years ago

The Gene Pool and Selective Breeding

  • The gene pool is the collection of all the different alleles held by an entire population
  • Selective breeding reduces the gene pool because breeders repeatedly select for specific alleles that code for desirable traits, gradually eliminating others
  • Over many generations, the gene pool becomes smaller and smaller as unfavourable alleles are removed from the population

Inbreeding: A Key Drawback

  • Because the best individuals often share similar genes and may be closely related, breeding them together can lead to inbreeding
  • Inbreeding makes offspring particularly prone to inherited diseases and genetic defects due to their very limited gene pool
  • Breeds such as German Shepherds and Rottweilers are examples of animals that suffer from health conditions as a result of a reduced gene pool caused by selective breeding

Reduced Variation: Another Disadvantage

  • A smaller gene pool means there is less genetic variation within the selectively bred population
  • If a new pathogen were to infect one individual in a low-variation population, it could potentially spread and affect all individuals, risking the loss of an entire crop or herd
  • This vulnerability to disease highlights why maintaining genetic diversity is important in farmed populations