Every creature possesses a multitude of genes, but not all features contained in DNA are ever expressed, that is, expressed. Some genes remain inactive but are present and can still be inherited. Depending on the genotype of the sexual partner, an unexpressed gene can appear in the generation of the offspring, ie be expressed.
When gene expression is always two identical genes in question, which each come from the mother and the father and in a way compete with each other. There is one dominant and one recessive gene. In humans, a dominant gene usually triumphs over a recessive or two recessive genes are equally expressed and produce a visible feature that lies between that of mother and father.
For example, in some plants, the colors red and white are both recessive, and when blended, pink flowers are produced in the progeny generation because gene expression of both genes occurs.
Man possesses a large number of genes on his total of 47 chromosome pairs. He has one half of his mother, the other half of his father, just like every creature. From an evolutionary point of view, it is now important to express those genes that are most helpful for the survival of the new human being.
For example, evolution has shown that gene expression of dark skin genes in sunny, warm regions of the earth is beneficial to humans, while gene expression of the fair-skin genes was better in less sunny parts of the world. In particular, in two recessive genes, it causes one or both of them to be expressed by gene expression, thereby enabling the species to steadily improve and become more viable.
Therefore, even in genetically identical, identical twins with two recessive genes slightly different features, such as the smallest differences in the hair or eye color.
So-called mutations of individual genes, ie spontaneous changes due to the constant formation of new body cells, have always occurred in almost every multicellular organism. In this way, for example, snow bunnies or polar bears have emerged: gene mutation led to the gene expression of white hair, the mutant animals proved to be more viable in polar regions than the brown conspecifics and prevailed in these parts of the earth. However, such processes, which rely on mutation-dependent alternating gene expression, take millennia and sometimes millions of years to become widespread.
Not only the gene expression of his own body, but also that of bacteria proves useful to humans. Using various antibiotics, it is possible, among other things, to inhibit the bacterium in its gene expression and thus to arrive at the failure of vital functions. The bacterium dies and the human can recover from a bacterial infection.
Furthermore, it is currently being investigated whether cancer-triggering genes can be inhibited in their gene expression so that genetically predisposed to cancer people do not form a tumor.
Gene expression is a complex process that, just like any genetic process in the body, can lead to disease. This applies both to incomplete or absent gene expression as well as to complete gene expression of defective genes.
Hereditary diseases of all kinds cause gene expression of a dominant or a diseased recessive gene in combination with a recessive gene of the healthy parent. Particularly hereditary diseases are hereditary diseases that do not break out in a sick and a healthy gene, because both parents are healthy, but carriers of the diseased gene. When both sick genes come together, gene expression by a healthy and diseased gene, or by the healthy, dominant gene, and the genetic disease breaks down.
An example of this is hemophilia, which occurs almost exclusively in men. Also considered to be dangerous are genetically modified substances that can alter gene expression in such a way that humans become ill or die. Radiation, for example, can change genes in every phase of human life in such a way that gene expression is different from before. This can lead to malformations caused by incorrect gene expression in adults for the later development of cancer and in unborn children.
Similar effects of erroneous gene expression by external, mostly chemical influences are also observed in animals and plants, which change their color or reproductive parts such as flowers and leaves differently than before.
A change in genes and thus deviations from the previous gene expression must also be excluded for medicines, they must not have any so-called mutagenic effects on humans or animals. The thalidomide scandal is a negative example in this regard.