Artificial Selection
This lesson covers:
- What artificial selection is
- Problems caused by inbreeding
- How outbreeding can maintain genetic diversity
Artificial selection
Artificial selection, also called selective breeding, is when humans breed organisms selectively for specific genetic traits and determine which individuals reproduce. It changes allele frequencies by favouring certain traits that then become more common over time.
How artificial selection works
Artificial selection uses the same principles as natural selection but, instead of the environment, humans choose the desired traits and the individuals that reproduce, leading to species that are beneficial to humans in some manner.
The process of artificial selection:
- Select a population that displays variation.
- Select individuals with desired traits, like high milk production in female cattle and male cattle with female relatives with high milk yields.
- Selectively breed individuals together that display these desired traits.
- Grow and test the offspring for the desired traits.
- Repeat the selection process across many generations.
This produces a population of individuals that all show certain desired characteristics and that can be further inbred to produce offspring with these characteristics.
For example, in plants, rice and wheat can be artificially selected to improve the following:
- To produce many different varieties of rice and wheat.
- To produce wheat grains that are rich in gluten.
- To produce varieties that have resistance to diseases like those caused by fungal infection.
Problems caused by inbreeding and the benefits of outbreeding
Although artificial selection can preserve desirable traits, it can also decrease genetic diversity due to inbreeding. The negative effects of this can be overcome with some degree of outbreeding.
| Inbreeding | Outbreeding | |
|---|---|---|
| Definition | The mating of closely related individuals, often a part of artificial selection | The process of breeding unrelated or distantly related individuals |
| Effect on genetic diversity | Decreases genetic diversity | Increases genetic diversity |
| Effect on heterozygosity | Reduces heterozygosity | Increases heterozygosity, protecting against harmful conditions caused by homozygous recessive genotypes |
| Effect on homozygosity | Increases homozygosity, leading to the expression of harmful recessive alleles | Decreases homozygosity, reducing the expression of harmful recessive alleles |
| What it can lead to | Inbreeding depression - the loss of ability to survive and grow well | Hybrid vigour - the increased ability to survive and grow well |
| Effect on fitness and adaptability | Reduces fitness and adaptability | Increases fitness and adaptability |
| Example in maize | Maize plants with inbreeding depression become progressively smaller | Hybrid vigour in maize plants makes them healthier, grow taller, and produce higher yields |
A balance of inbreeding and outbreeding can preserve desirable traits like crop uniformity for easier harvesting and selling, while still maintaining heterozygosity for better health and yield.