Artificial Selection
Biology: Cambridge International A Level, topic 17.2.7
Artificial Selection - Example
Artificial selection happens when humans choose animals and crops to breed, based on their genetic characteristics. The process of the artificial selection of big cows proceeds as follows:
1) Parent selection and breeding
- Choose parents who most strongly display the desired characteristic.
- Breed the chosen parents.
2) Offspring selection and breeding
- From the resultant offspring (children), choose the offspring that best display the desired characteristic.
- Breed these chosen offspring.
3) Repeat
- Repeat this process of breeding and re-selection over many generations until all the offspring show the desired characteristic.
History of artificial selection
- Humans have done this in farming for thousands of years (with both crops and animals) to promote the genetic characteristics that we view as desirable.
Uses of Selective Breeding
Usefulness and appearance are the two most common reasons for a characteristic being considered desirable. Some useful examples are:
Crops
- Disease resistance in food crops like wheat and rice is a useful characteristic because it improves yield (food production productivity).
- Mutant alleles for gibberellin synthesis can be selectively bred into plants to produce dwarf varieties.
- This increases crop yield as more energy is used to grow the grain rather than grow the plant taller.
- Maize crops have been hybridized & inbred to produce uniformity in groups.
- Hybridization involves crossbreeding different species of corn that each have desirable characteristics.
Animals
- In farming, animals that produce more milk or meat are also useful for yield-related reasons.
- This has been done with dairy cows. Cows have the amount of milk they produce (yield) recorded.
- This allows identification of bulls that produce female offspring with high yield.
- Eggs from high-yield female cows are inseminated by such bulls. The resulting embryos are placed in surrogate cows.
- This process is repeated over many generations to produce high milk yield cows.
Dogs
- Gentle-natured domestic dogs are useful as these animals must co-exist (live with) with humans.
Dangers of Artificial Selection
Artificial selection can create some issues:
Inbreeding
- Artificial selection can lead to inbreeding. Here, some breeds become particularly susceptible to disease or inherited defects.
- For example, French bulldogs have been selectively bred to have flat faces, but that causes them breathing problems.
Reduced variation
- Artificial selection can reduce variation (differences in characteristics) within a population, making it harder for a species to adapt to environmental change.
Test yourself on Artificial Selection
After breeding parents with the desired characteristic, what is the next step in the selective breeding process?
There are several steps involved in the selective breeding process. Which of the following apply to selective breeding?
Selective Breeding
What is getting strong, fast racehorses to reproduce an example of?
Which of these statements about the dangers of artificial selection are true?