Modern wheat, dairy cows and pedigree dogs look nothing like their wild ancestors. Farmers and breeders produced them by choosing which individuals were allowed to breed, generation after generation. This is selective breeding, or artificial selection. Comparing it with natural selection is Extended content.
In selective breeding (artificial selection) humans select individuals with desirable features, cross them to produce the next generation, and select the offspring showing the desirable features. Repeating this over many generations improves crop plants and domesticated animals. Extended: in natural selection the environment decides which individuals reproduce; in artificial selection humans decide.
The sim shows a field of 24 wheat plants with ears of grain of different sizes. Click the plants with the biggest ears (a ring marks each one), or press Pick the best 4, then press Breed from selected. Watch the generation count and the mean yield in t/ha, and the graph of mean yield.
Selective breeding only works on inherited variation. A plant that is large only because it grew in richer soil will not pass that on, which is why the sim's yield climbs gradually rather than in one leap.
Four quick checks. Each correct answer earns XP and records this skill on your profile.
In the wheat sim, which plants should you select to raise the yield?
What is the fewest number of plants you must select before you can breed?
After several rounds of selecting and breeding, what does the mean yield graph show?
Why do the offspring in each new generation still differ in ear size?
The same method is used for any feature people want, as long as it is inherited. In an exam, apply the three steps to the organism you are given.
| Organism | Desirable features selected |
|---|---|
| Wheat, rice, maize | high yield, resistance to disease, short stems that do not blow over, tolerance of drought |
| Fruit and vegetables | larger or sweeter fruit, longer shelf life |
| Dairy cattle | high milk yield |
| Beef cattle, sheep | fast growth, more meat, better wool |
| Dogs, horses | gentle temperament, speed, strength |
Extended. Both processes change the frequency of alleles in a population over generations. The difference is who, or what, does the selecting.
| Natural selection | Artificial selection | |
|---|---|---|
| What selects | the environment (predators, competition, disease, climate) | humans |
| Features selected | those that help the organism survive and reproduce | those useful or wanted by people, not necessarily good for the organism |
| Speed | usually slow, many generations | usually faster, as only chosen individuals breed |
| Result | populations adapted to their environment | improved crop varieties and animal breeds |
Artificial selection can make an organism less able to survive in the wild. Very high-yield crops may need fertiliser and pesticides, and some dog breeds have breathing problems.
Unlocks once the four checks above are done. Worth more XP, written to IGCSE Paper 2 and Paper 4 standard.
Which is the correct sequence for selective breeding?
A farmer wants sheep with thicker wool. Which sheep should be bred together?
Extended: which is a difference between natural selection and artificial selection?
Extended: a high-yield crop variety needs heavy use of fertiliser and pesticide. This illustrates that artificial selection:
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