Selective Breeding and Genetic Engineering
Compare selective breeding, which chooses parents and offspring over generations, with genetic engineering, which changes DNA directly. Explain inbreeding risk and assess benefits and concerns for examples such as insulin-producing bacteria and Bt maize.
What a learner can do afterwards
- Describes the repeated steps of selective breeding and says why it takes generations.
- Explains why mating close relatives can increase harmful recessive combinations and identifies a breeding plan that reduces this risk.
- States one benefit and one objection for a named engineered crop or bacterium.
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You have seen how parents pass alleles to offspring. Selective breeding uses inherited variation: choose parents with a wanted heritable trait, breed them, assess their offspring, then select parents for the next round. Dairy cattle, wheat and dogs have been selectively bred. Repeated selection takes generations because offspring must be produced and assessed before the next round. Results depend on inherited variation and growing or living conditions.
Inbreeding means mating close relatives. They are more likely to share alleles, including harmful recessive ones. Offspring are therefore more likely to inherit two harmful copies, though illness is not certain. Using very few parents can also reduce genetic variation. Outcrossing to unrelated animals tested not to carry a harmful allele can reduce harmful pairings in future offspring. Check other wanted traits too. This does not cure affected animals.
Genetic engineering changes DNA directly by inserting DNA or editing an existing sequence. An inserted gene need not come from another species. Crossing compatible parents and selecting offspring is selective breeding, including crosses between varieties or closely related species. Making and testing an engineered organism can take years. Neither method guarantees a useful result in one season.
Researchers can give E. coli bacteria a DNA sequence that lets them make human insulin. The insulin is collected and purified for medicine. Selecting unmodified E. coli cannot supply the human insulin-coding sequence absent from them. Engineering supplies DNA directly, but producing a usable medicine still requires controls and testing.
Bt maize contains a gene from Bacillus thuringiensis and makes a protein that harms certain insect pests. This can reduce pest damage. One concern is gene flow: pollen may pass the allele to plants that can cross with maize. Its effects depend on nearby compatible plants and what the trait does. Compare benefits and concerns for the named crop and setting.
Breeding selects inherited variation. Engineering changes DNA directly. Assess the trait, the time needed, and the benefits and concerns in each case.
Lesson, questions and flashcards written for this dataset.
Readings and flashcards written for this dataset. Video: Introduction to genetic engineering, Khan Academy.
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Making a DNA change useful
An engineered cell and a finished medicine are different products. Giving E. coli suitable insulin-coding DNA can let the bacteria produce human insulin. The protein then has to be collected, purified and tested. Selecting among unmodified bacteria cannot supply the human insulin-coding sequence absent from them.
Genetic engineering acts directly on DNA. Researchers may insert DNA or edit a sequence already present. Some inserted genes come from another species, but cross-species transfer is not required for every engineered change. Researchers must check both the DNA change and its effects.
A crop also needs assessment outside the laboratory. Bt maize makes a protein that harms certain insect pests, which can reduce crop damage. Its pollen may carry the allele to compatible plants. Whether this creates a problem depends on which plants are nearby and what happens when the allele is inherited. The crop's trait and setting matter when comparing benefits and concerns.
Selecting a trait across generations
A breeder needs inherited variation in the wanted trait. A plant's growth can reflect both its alleles and its growing conditions. Choosing a tall plant does not promise that all its offspring will be tall. Breeders assess offspring before selecting parents for another round.
Selective breeding follows this repeated cycle: choose suitable parents, produce offspring, assess their traits and select again. Cattle, wheat and dogs provide familiar examples. Successive generations are needed because each selection depends on producing and assessing the next offspring.
Selecting one trait does not remove the need to check others. Repeatedly using very few parents can reduce genetic variation. Mating close relatives increases the chance of shared harmful recessive alleles coming together in offspring. Unrelated animals and allele tests can help breeders avoid particular harmful pairings. These choices concern future offspring; they do not cure animals already affected.
Will offspring inherit a DNA change?
The words 'genetically engineered' do not tell you whether every offspring will inherit a change. In sexual reproduction, the relevant DNA must reach reproductive cells. A change confined to an ordinary body cell need not pass to offspring.
Even when an allele can be inherited, its transmission depends on the parents' genotypes. A plant carrying one changed allele and one unchanged allele may pass either one through a reproductive cell. The other parent also contributes an allele. Knowing that a parent was engineered is therefore not enough to predict every seedling's genotype.
Breeding can follow engineering. Researchers might first make a direct DNA change and then cross plants carrying it with a compatible crop variety. Making the DNA change is engineering; choosing crosses and selecting their offspring is breeding. Keeping these actions separate helps explain both how a trait was introduced and how it might spread.
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