What is selective breeding?

Selective breeding involves selecting parents that have characteristics of interest in the hope that their offspring inherit those desirable characteristics.

What is selective breeding?

  • Selective breeding involves choosing parents with particular characteristics to breed together and produce offspring with more desirable characteristics.
  • Humans have selectively bred plants and animals for thousands of years including:
    • crop plants with better yields
    • ornamental plants with particular flower shapes and colours
    • farm animals that produce more, better quality meat or wool
    • dogs with particular physiques and temperaments, suited to do jobs like herd sheep or collect pheasants.
  • Selective breeding aims to adapt an organism’s characteristics in a way that is desirable to the humans that breed them. 

Humans have selectively bred apples to create lots of different varieties.
Image Credit: Dllu via Wikimedia Commons

How does selective breeding work?

  • An organism’s characteristics are partly determined by the combination of gene variants that are passed on from one generation to the next. For example, the children of tall parents may themselves be tall if they inherit a combination of ‘tall’ gene variants.
  • We can take advantage of this to selectively breed animals or plants, choosing parents with particular characteristics to produce offspring that have those characteristics.
    • For example, if we breed tall parents together and exclude shorter parents, the offspring should inherit “tall” gene variants that make them tall.
    • Some of the offspring may even be taller than both of their parents, because they may inherit a combination of different “tall” gene variants from each parent and together these make the offspring taller.
    • With repeated selective breeding over multiple generations this population will get taller and taller.

A diagram showing the effect of selectively breeding for height in plants.
Image Credit: Genome Research Limited

 Problems with selective breeding

  • Selective breeding often results in a population of animals or plants with very similar genetics.
  • Similar genetics means that the population will have the same strengths but also the same weaknesses.
  • Infectious diseases are more likely to spread through genetically similar populations because they are vulnerable to the same diseases.
  • Selective breeding often involves breeding individuals that are closely related, known as inbreeding.
    • Inbred populations are more likely to suffer from genetic conditions caused by recessive gene variants because they are more likely to inherit two copies of the recessive variants, one from each parent.

 Types of selective breeding

Inbreeding

  • If we want to establish a population of organisms with predictable characteristics we tend to “inbreed”.
  • Inbreeding is when the animals bred are very close relatives, such as siblings.
  • Continued inbreeding results in offspring that are very genetically alike.
  • After many generations of inbreeding, the offspring will be almost genetically identical, and will produce identical offspring. When this happens, an organism is described as inbred or purebred.
  • Examples of purebred animals are Labrador Retriever dogs and Siamese cats.

Purebred dogs like the Labrador Retriever were originally established through many generations of inbreeding.

Linebreeding

  • Linebreeding is a type of inbreeding.
  • It involves breeding together more distant relatives, such as cousins.
  • This reduces the rate at which the breed becomes ‘purebred’, reducing the risk of ill-health that can sometimes be seen with purebred individuals. 

 Self-pollination

  • Most plants have both male and female reproductive parts.
  • Some species are naturally able to transfer the male gametes (sperm) in the pollen to the female parts of the flower where the female gametes (eggs) are. This is called self-pollination.
  • The offspring of plants that self-pollinate are not identical to the parent plant, because their genes are shuffled during reproduction.
  • Plant breeders can use self-pollination as a type of inbreeding, creating plants that are genetically more identical and that produce identical offspring after many generations.

 Crossbreeding 

  • Crossbreeding involves breeding two unrelated individuals.
  • This is often used to produce offspring with desirable characteristics from two different individuals.
  • Crossbreeding two purebred organisms will produce offspring that display the characteristics of interest.
  • For example, Poodles are crossed with Labrador Retrievers to combine a Poodle’s low-shedding coat with the Labrador’s calm, trainable temperament. The resulting ‘Labradoodle’ is a guide dog suitable for people with allergies.
  • Crossbreeding non-purebred parents will have less predictable outcomes.

The Labradoodle is a crossbred dog resulting from breeding a Labrador with a poodle

Selective breeding versus natural selection

  • Although they both result in genetic changes over generations, selective breeding and natural selection are different.
  • Natural selection is driven by environmental factors that limit survival and reproduction, such as harsh environments or competition for mates.
  • Selective breeding is also known as artificial selection. Artificial selection is driven by human intervention.

 Selective breeding versus genetic engineering

  • Although both selective breeding and genetic engineering change an organism’s genetic characteristics, they are different processes.
  • Selective breeding makes use of existing, naturally present gene variants in a species and the natural process of breeding.
  • Genetic engineering involves a direct change to an organism’s genome in the laboratory.
  • Gene variants made through genetic engineering can be passed from one generation to the next.

This page was last updated on 2017-03-03