4.10.8Additional lessons
Artificial Selection — IB Biology HL Revision Notes & Topical Questions
5 min read 5 parts Lesson 91 of 101
Section 1 of 5Process of Artificial Selection
Artificial selection uses the same genetic principles as natural selection, but humans decide who reproduces.
Choosing
- People select individuals with desired heritable traits, such as high milk yield or large fruit, as parents.
Breeding
- Only the chosen individuals are allowed to reproduce, so their alleles are passed on.
Repetition
- Selection is repeated for many generations, which gradually shifts the traits of the population.
Result
- The population differs strongly from its wild ancestors, as seen in crop plants and domestic animals.
| Feature | Natural selection | Artificial selection |
|---|---|---|
| Selecting agent | Environment | Humans |
| Favoured trait | Increases survival in the wild | Useful or attractive to people |
| Speed | Usually slow | Often faster |
| Result | Adaptation to habitat | Traits that may reduce wild fitness |
| Genetic variation | Needed in both, and may fall under strong artificial selection |
Section 2 of 5Example: Brassica oleracea
1
Wild cabbage, native to coastal Europe, shows natural variation in leaf size, stem thickness and flower arrangement.
2
Farmers choose plants with large terminal buds and breed from them, which leads to the cabbage.
3
Selecting for swollen flower clusters gave cauliflower and broccoli, and enlarged lateral buds gave Brussels sprouts.
4
Selection for thickened stems produced kohlrabi and for leaf quality produced kale, all from one species.
Section 3 of 5Benefits and Risks
Benefits and Risks
Benefits
- Higher yields, disease resistance and better quality increase food supply and farm income.
Reduced diversity
- Breeding from few individuals shrinks the gene pool and increases the chance that harmful recessive alleles appear.
Vulnerability
- Genetically uniform crops can all be lost to a single new disease or pest.
Welfare
- Some animal breeds suffer health problems, such as breathing difficulties, from extreme selected features.
Section 4 of 5Worked Example
Question
- A dairy herd produces a mean of 4 000 litres of milk per cow per year.
- After 10 generations of selective breeding the mean is 5 500 litres.
- Calculate the total percentage increase and the mean increase per generation.
- Increase = 5 500 − 4 000 = 1 500 litres.
- Percentage increase = 1 500 ÷ 4 000 × 100 = 37.5%.
- Mean increase per generation = 1 500 ÷ 10 = 150 litres.
Answer 37.5% overall, which is 150 litres per generation.
Section 5 of 5Exam Checklist & Tips
4.10.8 – Key Points for the Exam
- Artificial selection Choice of breeding individuals by humans to change heritable traits.
- Selective breeding Another term for artificial selection.
- Inbreeding Mating between closely related individuals.
- Monoculture Large area planted with genetically uniform crops.
- Domestication Adaptation of a species to life with humans through selection.
Common Mistakes
- Saying that artificial selection creates new alleles;
- it selects from existing variation, although mutations may arise.
- Writing that traits chosen always help the organism to survive in nature.
- Forgetting to state that the trait must be heritable.
- Describing the different Brassica vegetables as different species.
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