Plant breeding and genetic engineering are incredibly useful tools. Like most tools, they serve distinct purposes. Plant breeding randomly combines the genes of two closely related plants. This is useful when both parents have several useful traits. Genetic engineering allows scientists to move specific genes between species. I used the following scenario to demonstrate the precision of genetic engineering as compared to plant breeding to freshmen at San Marin High School:
Two volunteers were selected to be “genetic engineers” and the remaining 15-20 students were “plant breeders”. Each student was given two solo cups, one representing maize (corn) and one representing its wild ancestor teosinte. Each cup contained six Popsicle sticks each representing a gene. The bottoms of the Popsicle sticks were colored green, yellow, or red. The colors represented useful genes, neutral genes (conserved between corn and teosinte), and undesirable genes respectively. Corn had three useful genes and three neutral genes. Teosinte had one useful gene (the disease-resistant trait), two neutral genes, and three undesirable genes.
Students were instructed to “make a cross” between these two species by selecting three Popsicle sticks from each cup. “Genetic engineers” had clear cups and could pick the genes they wanted. “Breeders” had red cups and had to randomly select their genes. The goal was to maximize the number of useful traits and avoid any undesirable traits.
Each of the genetic engineers selected four useful genes and two neutral genes. Breeders ended up with a variety of different combinations. Only one breeder successfully avoided picking any red Popsicle sticks; however, this student still ended up with less total positive/green traits than the genetic engineers.
The students asked what a breeder would do to generate the same optimized crop as the genetic engineers. The “breeder” whose new crop had no undesirable traits put his Popsicle sticks into a new cup and then “back-crossed” it with maize (again randomly selecting three popsicle sticks from each). After two rounds, he still had not managed to generate a variety with as many good traits as the genetic engineers. I then went on to explain that this scenario assumes there are only six genes in corn and that each of those genes acts independently. In fact there are over 30,000 genes and neighboring genes tend to be inherited together.
Hands-on Activity: Breeding Vs Genetic Engineering by Jenna E Gallegos is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
Based on a work at https://escapingthebench.wordpress.com/2016/03/20/hands-on-activity-central-dogma-of-biology/.