A gene is a structural and functional unit of heredity in living organisms. A gene is a piece of DNA. The specific location of a gene on a chromosome is called a locus. Most genes are recipes for making proteins. It is surprising to admit that a person does not inherit genetically, for example, high intelligence, but only the ability to develop his brain to a certain level, and then only if the right conditions are created. By the way, he has every right not to use this ability. Each gene is represented by two or more varieties, or specific states — alleles, alternative versions of the same gene, among which there are neither good nor bad. The concepts of “gene” and “allele” are synonymous to a certain extent. A gene is a broad concept, an allele is more specific. The set of genes that a living organism received at birth makes up its genotype. This is a complete set of genetic information. The same genotype is found in identical twins. The totality of the hereditary material contained in an organism’s cell is called a genome. According to various estimates, the total number of genes in the human genome ranges from 26,383 to 43,162, although there is information about only 20-25 thousand genes.. Before decoding the human genome, it was believed that there were dozens of times more of them. Anyway, twenty thousand is a lot. “The genome that our generation has managed to open and read is just a snapshot of an ever—changing document that will never have an up-to-date edition.” Matt Ridley Understanding how everything works, we can boldly say that genes are eternal. The life of each individual DNA molecule is quite short, usually no more than a few months, and certainly no longer than the life span of a human. But a DNA molecule can continue to exist as copies of itself for 100 million years. In addition, copies of a single gene can spread all over the world. The defining property of a gene is its potential immortality in the form of copies. The gene has the necessary properties — durability, fertility, and copy accuracy. What exactly does durability mean? It depends on how strong the influence of natural selection is — how much more likely is the death of a “bad” genetic unit, rather than its “good” allele. A gene can be defined as a region of a chromosome that is potentially able to persist for a long time and function as a significant unit of natural selection. In classical genetics, a gene is an abstract concept, a unit of inheritance that transmits certain qualities from parent to child. Biochemistry has brought specifics to this picture: these qualities are associated with enzymes and proteins, one for each gene. And with the advent of the era of molecular biology, genes found their embodiment in a material substance — a DNA sequence, which, when converted into informational RNA, can be used as the basis for creating proteins. Genes can change — this is called mutation susceptibility. It is gene mutations, not their presence, that cause certain diseases. The effectiveness of treatment depends on the characteristics of the body, a fact that is very reluctantly accepted by pharmacists and doctors who prefer to treat humanity rather than humans. A drug that is effective for one patient may be useless for another. A diet that can save one person’s life may be meaningless for another. The medicine of the future is based on the analysis of the patient’s genotype before prescribing treatment.