5b Selective Breeding¶
Part of 5 Use of Biological Resources.
Selective breeding uses inheritance knowledge to increase the frequency of desirable characteristics in plants and animals. The benefits are clear, but so are the genetic risks if variation is reduced too far.
Learning Objectives¶
| ID | Official specification wording | Main teaching sections |
|---|---|---|
5b-lo-1 |
5.10 understand how selective breeding can develop plants with desired characteristics | How Selective Breeding Works, Uses in Plants and Animals |
5b-lo-2 |
5.11 understand how selective breeding can develop animals with desired characteristics | Uses in Plants and Animals, Limits of Selective Breeding |
How Selective Breeding Works¶
Selective breeding (artificial selection) is the process by which humans choose which organisms to breed in order to produce offspring that express a desired characteristic. The process has been practised for thousands of years since animals were first domesticated and plants grown for food.
The steps are: 1. Parents that show the desired characteristic most strongly are chosen from the population. 2. They are bred together. 3. From the offspring, those that show the strongest expression of the desired characteristic are selected and bred together. 4. This process is repeated over many generations.
Over time, the alleles associated with the desired characteristic become more frequent in the population. The characteristic becomes increasingly pronounced in successive generations.
Uses in Plants and Animals¶
Selective breeding can be applied to any heritable characteristic: - Plants: larger fruits, higher grain yields, disease resistance, drought tolerance, more vigorous growth. - Animals: higher meat yield, greater milk production, disease resistance, specific coat or behavioural traits, increased egg production.
Limits of Selective Breeding¶
Selective breeding concentrates certain alleles but necessarily reduces others. This creates several risks:
- Reduced gene pool: selecting for the same set of desirable alleles means breeding closely related individuals — the variety of alleles in the population (the gene pool) decreases.
- Inbreeding: closely related individuals are more likely to share the same recessive alleles. Offspring become more likely to be homozygous for those recessives, making harmful recessive conditions more likely to appear.
- Vulnerability to disease and environmental change: a population with limited genetic variation has less chance that any individual will carry an allele that provides resistance to a new disease or adaptation to a changed environment. If conditions change or a new pathogen emerges, the entire population may be susceptible.
Common Confusions¶
- Selective breeding vs genetic modification: Selective breeding works within a species, using existing alleles. Genetic modification can introduce entirely new genes from other species.
- Short-term benefit vs long-term risk: Selective breeding can produce rapid improvement in a desired trait but can simultaneously create genetic weakness if diversity is too heavily reduced.
Key Terms¶
- Selective breeding: the process of choosing organisms with desired characteristics and breeding them over many generations to increase the frequency of that characteristic.
- Desired characteristic: a heritable trait that breeders wish to increase in a population.
- Inbreeding: breeding between closely related individuals, which reduces genetic diversity.
- Gene pool: the complete set of all alleles present in a population.
- Artificial selection: another term for selective breeding — human-directed selection for particular traits.