Since time immemorial, people have been interested in why some children resemble their parents more than others, or why certain diseases occur more often in some families than in others. Similar questions are asked when growing plants and raising animals. People have subsequently tried to use their observations in order to obtain offspring with the most suitable characteristics. Questions like: "Why do ornamental plants offer so many colors and shapes?" or "Is it possible to somehow increase the yields of commonly grown crops?" were also dealt with by an Augustinian monk working in nearby Brno in the 19th Century, Gregor Johann Mendel (Figure 1.1). His curiosity led him to patiently search for answers to these questions in long-term experimental work. Perhaps his origin also predestined him for this, as he came from a peasant family that was engaged in agriculture and was therefore close to nature. Through experiments with plants, Mendel wanted to understand the principles of inheritance of various characteristics of plants and animals, and we can say today (almost two hundred years later) that he was successful in his endeavor.