Genetic engineering: The road to precise editing of DNA

Humans have directly influenced the modification of DNA in organisms for thousands of years through domestication and selective breeding. You can see the outcomes of these actions in our homes, farms, and factories. These methods of changing the DNA of living organisms take advantage of evolution. When humans cross-breed plants, the DNA within the plants mix: DNA from one plant will combine with another.

The result is modified DNA with new traits that may or may not be beneficial to the plant. With human intervention, however, if the new trait is beneficial and desired by the human, it becomes selected for because the plant’s survival will be encouraged by humans through watering, and propagating the plant’s seeds. Because of this, plants, especially crop plants such as maize (corn) are almost unrecognizable when compared to their ancestors (Figure 1-12).

Figure 1-12. Comparison of modern Com (maize) (bottom), its ancestor Teosinte (top) and a hybrid of both (middle)

Domestication and selective breeding do not only apply to crops. Consider pets for a moment. The “original dog” is Canis lupus, better known as the wolf. Dogs have been so extensively bred by humans that a huge dog such as a Great Dane—standing at a minimum of 3 feet and weighing almost 250 pounds—can no longer physically mate and reproduce in nature with a small dog such as a Chihuahua—standing at less than 1 foot and weighing less than 10 pounds.

The Chihuahua is 25 times smaller than the Great Dane, yet both are descendants from the same source DNA (Figure 1-13). In the natural world, these two organisms can no longer effectively breed. Their DNA can no longer combine and intermix as would naturally happen in a species. Without human intervention, this will eventually lead to the development of two different species. This is evolution in progress.

Figure 1-13. Great Dane skeleton (left) compared to a Chihuahua skeleton (right), both descendants of Canis Lupus, at the Museum of Osteology

The methods in which humans evolve plants and pets through deliberate breeding and selection extends into all corners of the natural world - trees, grasses, flowers, livestock animals, and even microorganisms. Much of the food we eat today was evolved through selective breeding by humans. This process often takes a long time because “DNA mixing” through these methods is random, and desirable traits only appear by chance. What if randomness could be taken out of the equation? What if humans could, with extreme precision, edit DNA?

The precise engineering of organisms is the focus of this book. By its end, you will have gone through exercises where you will have precisely changed an organism’s DNA to get a desired trait. Over the past 100 years, humans have made ground-breaking discoveries that have led us to understand what DNA is, how DNA behaves, and its importance in biology.

These discoveries have led to new technologies that enable us to precisely read, write and edit the DNA of organisms. There has also been a change in the mindset of people. No longer is nature and the natural world seen as being immovable or unchangeable. A robust engineering discipline has emerged where we can now make very important things using biology. We call this the Biology-as-a-Technology mindset.

The knowledge and skills imparted by this book are not to be taken lightly. Understanding how DNA and cells interact will be vital to making informed decisions about using your new skills. Now that you have seen DNA and know that it can be manipulated let’s further explore the building blocks of DNA and the cells where they reside.