## Targeted change of the organism's genetic information

GMOs are organisms whose DNA has been modified in a way that is not possible in nature, and genetic engineering methods are usually used for this purpose. In addition to these methods, however, humanity has had another very effective approach to DNA modification of various types of organisms – breeding. By breeding we mean the intentional selection of individuals (mostly plants or animals, in specific cases also microorganisms) with similar characteristics (e.g., the size of plant fruits or the amount of muscle processed into meat in cattle), which can be crossed with each other. From the offspring, individuals can be selected which have the most suitable characteristics, and the process repeated many times. It is obvious that in this way people purposefully (because they carry out selection) change the genetic information (most of the characteristics of each organism are determined by genes) of the given organism even without laboratory equipment. Using this approach, it was possible to breed different races of dogs (the ancestor of all dogs was similar to a wild wolf), cattle or other animals (Figure 17.1).

If we look at the well-known Belgian blue cattle (Fgure 17.2) with today's technical knowledge, we will find that the enormous amount of muscle produced by these animals is due to a mutation in gene encoding the myostatin protein.This protein inhibits the building of muscle and ensures that the body's muscular system is appropriate for its overall constitution. In the case of Belgian blue cattle, this gene is mutated so that myostatin is not functional and consequently the cattle produce an extreme amount of muscle. When the breeding process of this type of cattle began, the mutation appeared randomly, but thanks to its physiological consequences, the individuals with the mutation were selected and further bred. After some time, the originally wild species has become, at least at a first glance, a completely different organism. Obviously, its special properties are caused by changes in genetic information, even though the breeders probably did not understand that at the beginning. Many other organisms have gone through a similar process in the past, including corn – a typical example of a plant species bred over thousands of years (breeding began around 5000 BC). The original ancestor of corn – teosinte – is a plant with a similar fruit structure, but significant differences in the number of seeds, their shape and size. All these characteristics (determined by genetic information) have been gradually modified by humans to create the corn we know today.

Therefore, it is clear that humans have influenced the genetic makeup of economically important domesticated plants and animals since the distant past. But why don't we consider these organisms GMOs? The answer is hidden in the second part of the definition, which says that an organism is considered a GMO only if the changes in its genetic information could not have occurred naturally. In the case of breeding, of course the changes did not occur in a natural way since the crosses were carried out by breeders according to their breeding intention. On the other hand, we must ask ourselves the question: "Could the two organisms that we selected for breeding, at least theoretically, meet freely in nature and have the offspring that we obtained?" To this question, in the case of bred organisms, we must answer: "Yes, it is theoretically possible, even though extremely unlikely.” As a result, we do not consider bred species of plants and animals to be GMOs, despite the fact that their genetic information has been altered by humans.