People have shaped the genes of plants and animals for thousands of years, using what you learned in Punnett Squares and Mutations long before anyone knew about DNA.
Key idea
In selective breeding, people choose which plants or animals become parents, generation after generation, so a wanted trait becomes more common. It works with variation already in the population. In genetic engineering, scientists move a specific gene into another organism, which then makes that gene's protein.
Why it works
Selective breeding uses natural variation: some corn plants have bigger ears because of the alleles they carry. Choose those as parents and their alleles become more common in the next generation. It cannot add a gene the population does not have. Genetic engineering can, because it moves DNA itself. The genetic code is the same in nearly all living things, so bacteria can read a human gene and build the human protein.
Worked example: One plant, many vegetables
Broccoli, cabbage, kale, cauliflower and Brussels sprouts are all one species, Brassica oleracea. How?
- Wild cabbage varies: some plants have bigger leaves, some bigger buds, some thicker stems.
- Over many generations, growers in different places chose different traits.
- No new genes were needed; choosing among existing variation changed each line.
Answer: Selective breeding for different traits from the same wild plant.
Worked example: Insulin from bacteria
In 1982, the FDA approved the first human insulin made by genetically engineered bacteria. Why use bacteria?
- Bacteria multiply quickly and are easy to grow in large tanks.
- With the human insulin gene inserted, each cell makes the human protein.
Answer: They are fast, cheap protein factories once they carry the human gene.
Common mistake
Students think selective breeding creates new genes. It only changes how common existing alleles are. New alleles come from mutations; moving a specific gene from another species is genetic engineering.
People weigh the uses of genetic engineering in food and farming differently. The science above is well established; how and where to use it is a choice communities discuss.