## From Mendel to the present

One of the reasons why the public initially did not understand Mendel's laws was perhaps the fact that at the time, it was not possible for scientists to find out which molecule in the cell is the carrier of these hereditary characteristics. Mendel's conclusions were thus forgotten for some time, but fortunately not for very long. At the beginning of the 20th century, specific formations - chromosomes - were discovered in the sex cells of plants and animals, whose behaviour during cell division and gamete formation corresponded to the behaviour of hereditary factors in the experiments described by Mendel. This discovery, together with the experiments of three important botanists - Hugo de Vries, Carl Correns and Erich Tschermak von Seysenegg - helped to rediscover Mendel's laws. Further important discoveries were not long in coming. Once the DNA molecule was identified as the material carrier of genetic information, genetics was transformed into an independent scientific discipline, and research in this area began to progress by leaps and bounds. The influence of many discoveries related to genetics and molecular biology on our everyday lives can no longer be underestimated. In this book, we will explain the secrets of genetics and point out significant discoveries and applications that each of us may encounter in our everyday life.

Right at the beginning, we will take a closer look at how a scientist works (Chapter 2). The public often imagines scientists as people who wear white coats, thick glasses, are oblivious to their surroundings and hold smoking test tubes of coloured liquid in their hands. However, real scientists, in contrast to this stereotypical image, use a wide range of approaches (many of which do not require test tubes or white coats at all) to solve various professional and practical problems. More than this, scientists are united by a scientific way of thinking, which is crucial in the design of experimental tests, but in many ways also facilitates everyday life.

In the section “Meet DNA: the bearer of genetic information“ (Chapter 3) we will take a closer look at the DNA molecule as the carrier of genetic information and its spatial structure. We will also describe how genetic information is realized - how the information stored in DNA is transcribed into RNA, and then proteins are created according to it, which perform the necessary activities in cells.

Are you interested in how scientists obtain material for genetic analysis, or how they navigate the vast amount of information written in DNA? Would you like to know how it is possible to "read" the DNA sequence and write it in the form of ordinary letters? Turn to Chapter 4 - How do you work with DNA. In this chapter you will find answers to these questions, as well as the principles of the most used methods, which geneticists and molecular biologists rely on in their research. In addition to basic research, these methods are also used in diagnosis of disease, food inspection, genealogical studies, archaeology and many other disciplines.

As mentioned above, Mendel's work was not properly received and appreciated during his lifetime, likely because variability played a significant role in his experiments. Today, it is already clear that DNA is not a static molecule, on the contrary, it is surprisingly dynamic and undergoes daily changes. These changes can cause DNA damage that, if not repaired, leads to mutations. You can read how DNA damage becomes a mutation and what effect it can have on the organism in Chapter 5 - Mutations - how they arise and what to do with them.

The information stored in the DNA (genotype of an individual) is important for the development of the organism. However, the resulting external manifestation of the genotype (phenotype), i.e., what an individual looks like, what characteristics it has and how it behaves, is also dependent, to some extent, on the external environment. Research in this area already indicates that the expression of many genes can be influenced by external factors. The scientific field of epigenetics deals with this kind of research. The basic principles of epigenetics, as well as issues of the influence of the environment on the activity of genes in a multicellular organism, are covered in Chapter 6 - How the environment can affect our genes.

A lot is already known about the fact that hereditary factors are responsible for the emergence of many human diseases. However, much less is known about the role of epigenetics in this context. Knowledge from this scientific field can help us understand many of our health problems. The ambition of Chapter 7 – From epigenetics to human diseases, is to present the influence of the environment and nutrition on our health, with a focus on individual phases of human life, heredity based on the experiences of previous generations, as well as heredity tied to a specific parent. The disease examples described in this section demonstrate why epigenetics as a modern, progressive scientific discipline deserves the attention of the general public.

Almost everyone knows stress as a widespread phenomenon of modern times. Most of us have already experienced a state where, under extreme mental or physical pressure, we feel a rush of adrenaline and for a moment we feel that we can handle everything. But with long-term exposure to stress, things change for the worse. Lack of sleep, irritability and mood swings are the order of the day for stressed people. All this negatively affects the physiological processes taking place in our body, which ultimately affects our health. But did you know that even individual cells can be under stress? And not only our human cells, but also the cells of plants, animals, even microorganisms. In Chapter 8 – Your cells are stressed too, we will therefore focus on cell stress. We will talk a little more about how and why it is produced, why it is necessary for cells, and what effect it can have on them if there is too much of it.

One of the most important topics of modern biomedicine, related to the content of several previous chapters, is cancer. Cancer has been linked to humanity since time immemorial, and along with it, people's efforts to understand its principles and discover a method of treatment. In Chapter 9 - When cells go crazy, we explain how and why a healthy cell becomes a tumour cell, what types of tumours we know and what therapy options are available for them.

Since various genetically determined diseases - among them some types of cancer - are currently among the most widespread health problems in the developed world, we focus on a promising technology that aims to replace or repair faulty genes and thereby eliminate the cause of the disease in Chapter 10 - Gene Therapy. In other words, how can gene therapy allow the treatment of so-called incurable diseases. In addition to cancer, these are mainly cardiovascular and neurodegenerative diseases or diseases of the musculoskeletal system. But why are we learning about gene therapy only now? Why is it not a regular part of our lives? The reason is that this promising technology also hides several potential pitfalls, which you can learn more about in this chapter.

Plants, like all organisms, constantly produce essential substances without which they would not survive (including sugars, fats and proteins). In addition, plants are able to produce compounds known as secondary metabolites, or phytocompounds, which although not essential for their survival, play a number of important roles, including signalling, protection against pathogens or attracting pollinators. However, these phytocompounds may not only be beneficial for plants, but also have meaning for humans. Many currently commercially available drugs originate from these plant components and, thanks to their wide spectrum of biochemical properties, find application in several branches of medicine and pharmacy. In Chapter 11 - Plants as an inspiration in biomedicine, we will imagine why and how such substances are formed in plants and explain with examples how we can use them to our advantage.

All living organisms, including humans, are in an environment in which they are surrounded by a wide range of substances. Some of them, whether natural or man-made, can have an adverse effect on us. In Chapter 12 - When the environment changes our hormones, we will look at substances that can affect the endocrine system and its proper functioning. Since hormones, as products of the endocrine system, regulate a number of processes in our body, their incorrect secretion or altered properties can lead to an undesirable physiological response of the body. How substances with excessive occurrence in the environment can change processes regulated by hormones will be explained using the example of bisphenol A, which is used for the production of plastics and is currently considered a virtually ubiquitous environmental pollutant.

Decent behaviour, ethics, or etiquette are a long-term part of civilized humanity. In fact, the term "behaviour" does not apply only to humans, but also to other living organisms, including the smallest ones - microorganisms. The genetic nature of this phenomenon is investigated by the genetics of behaviour (behavioural genetics). In Chapter 13 - Etiquette in our genes, you'll learn why it's good to study insect behaviour and whether our intelligence, sexuality, and behaviour are rooted in our genes or just a result of our upbringing.

Many years have passed since Charles Darwin published his work "On the Origin of Species by Means of Natural Selection" in 1859, and during that time the theory of evolution has become a relevant scientific theory. However, not everyone knows what principles this theory is based on, what is the real driving force of evolution, or how natural selection works. We will answer these and other questions in Chapter 14 - The principle of evolution.

Knowledge from the field of genetics has found its application not only in science and medicine, but its use covers various areas of life. Identification of persons based on DNA analysis is the essence of forensic genetics, is addressed in Chapter 15 - DNA as evidence. In this chapter, you will be able to take a look at the work of forensic scientists and criminologists who, based on knowledge of the DNA sequence, can recognize unknown persons and obtain incriminating evidence to identify the perpetrators of crimes.

Almost everyone who is involved in sports would like to win a race at least once. But how to achieve this goal? Is it enough to train persistently, or does success also depend on our genes? So far, approximately 200 genetic markers that influence sports performance have been identified. Some represent an advantage for endurance sports, others for speed or power. In Chapter 16 – Genetics in sport, we will talk about the variants of these genes and whether we need genetic testing when choosing a sports discipline.

Genetically modified organisms, which are covered in Chapter 17, are already around us today in the form of food, producers of drugs and hormones or in a scientific research environment. It is likely that in the future human society we will encounter this type of organism more and more often, so it is important for all of us to have at least a basic awareness of what a "genetically modified organism" actually is, what properties it has and what it is used for.

Vaccines cause autism! All people with blond hair will disappear within 200 years! Humans evolve from monkeys! There is a lot of information on the Internet that appears to be fact, but upon closer examination, it turns out to be untrue. Such false information does not bypass genetics either. Chapter 18 - The Most Common Hoaxes in Genetics: Myths and Facts, provides an overview of such false information and attempts to explain why it is incorrect or nonsensical. Knowing some characteristic features of false information can be important not only for processing knowledge from the field of biology, but also in everyday life.

Genetics as a science, but also as the basis of various modern technologies, is often depicted in pop culture - in films, books or computer games. In some cases, science fiction is elaborate and based firmly on scientific knowledge. In others, the term "genetics" is used as a magic word to justify the most incredible characteristics of the main characters. But how are we to distinguish between what makes sense on the TV screen, for example, and what is just a cheap stereotype? In Chapter 19 - Genetics in science-fiction and pop culture, we will use specific examples to show different ways of presenting genetics, thanks to which you too will learn to distinguish interesting fiction from superficial cliches.

To finish, chapter 20 takes a look at some key model organisms used to better understand the basis of genetics and biology more widely. You might be surprised at how diverse the organsims used are!