Our world is inhabited by a variety of organisms: from microscopic, visible only through a powerful microscope, to huge, weighing several tons. Despite such species diversity, all organisms on Earth have a very similar structure. Each of them consists of cells, and this fact unites all living beings. At the same time, it is impossible to meet two identical organisms. The only exception is identical twins. What makes every organism living on our planet so unique?
In every cell there is a central organ - this is the nucleus. It contains certain material units - genes located in chromosomes. From a chemical point of view, genes are deoxyribonucleic acid, or DNA. This double helix macromolecule is responsible for the inheritance of many traits. Thus, the meaning of DNA is the transfer of genetic information from parents to offspring. In order to deduce this truth, scholars of allthe world for two centuries made incredible experiments, put forward bold hypotheses, failed and triumphed from great discoveries. It is thanks to the work of great researchers and scientists that we now know what DNA means.
By the end of the 19th century, Mendel established the basic laws of the transfer of traits in generations. The beginning of the 20th century and Thomas Hunt Morgan revealed to mankind the fact that hereditary traits are transmitted by genes that are located on chromosomes in a special sequence. Scientists guessed about their chemical structure in the forties of the twentieth century. By the mid-fifties, the double helix of the DNA molecule, the principle of complementarity and replication, was revealed. In the 1940s, scientists Boris Ephrussi, Edward Tatum, and George Beadle made the bold hypothesis that genes produce proteins, that is, they store specific information about how to synthesize a specific enzyme for certain reactions in the cell. This hypothesis was confirmed in the works of Nirenberg, who introduced the concept of the genetic code and deduced a pattern between proteins and DNA.
DNA structure
In the nuclei of cells of all living organisms there are nucleic acids whose molecular weight is greater than that of proteins. These molecules are polymeric, their monomers are nucleotides. Proteins are made up of 20 amino acids and 4 nucleotides.
There are two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Their structure is similar in that both substances contain a nucleotide: a nitrogenous base, a phosphoric acid residue andcarbohydrate. But the difference is that DNA has deoxyribose and RNA has ribose. Nitrogenous bases are purine and pyrimidine. DNA contains the purine adenine and guanine and the pyrimidine thymine and cytosine. RNA includes in its structure the same purines and pyrimidine cytosine and uracil. By combining the phosphoric acid residue of one nucleotide and the carbohydrate of another, a polynucleotide skeleton is formed, to which nitrogenous bases cling. Thus, quite a lot of different compounds can turn out, which determine the species diversity.
DNA molecule is a double helix of two large polynucleotide chains. They are linked by a purine of one chain and a pyrimidine of another. These connections are not accidental. They obey the law of complementarity: bonds are able to form between themselves an adenyl nucleotide with a thymylic one, and a guanyl one with a cytosyl one, since they complement each other. This principle gives the DNA molecule the unique property of self-replication. Special proteins - enzymes - move and break hydrogen bonds between the nitrogenous bases of both chains. As a result, two free nucleotide chains are formed, which are completed by the free nucleotides available in the cytoplasm and nucleus of the cell according to the principle of complementarity. This leads to the formation of two strands of DNA from one parent.
The genetic code and its secrets
DNA research allows us to understand the individuality of each organism. This can be easily seen from the example of tissue incompatibility in organ transplants fromdonor to recipient. A "foreign" organ, for example, donor skin, is perceived by the recipient's body as hostile. This starts a chain of immune reactions, antibodies are produced, and the organ does not take root. An exception in this situation may be the fact that the donor and recipient are identical twins. These two organisms originated from the same cell and have the same set of hereditary factors. During organ transplantation, in this case, antibodies are not formed, and almost always the organ takes root completely.
The definition of DNA as the main carrier of genetic information was established empirically. Bacteriologist F. Griffiths conducted an interesting experiment with pneumococci. He injected a dose of the pathogen into mice. The vaccines were of two types: form A with a capsule of polysaccharides and form B without a capsule, both heritable. The first species was thermally destroyed, while the second did not pose any danger to mice. What was the bacteriologist's surprise when all the mice died from form A pneumococci. Then a reasonable question arose in the scientist's head about how the genetic material was transferred - through protein, polysaccharide or DNA? Almost twenty years later, the American scientist Oswald Theodor Avery managed to answer this question. He set up a series of experiments of an exclusive nature and found that with the destruction of a protein and a polysaccharide, inheritance continues. The transfer of hereditary information was completed only after the destruction of the DNA structure. This led to the postulate: the molecule carrying hereditary information is responsible for the transmission of hereditary information.
DNA structure revealedand the genetic code has allowed humanity to take a tremendous step forward in the development of such areas as medicine, forensics, industry and agriculture.
DNA analysis in forensic examination
Currently progressive record keeping of criminal and civil processes is not complete without the use of genetic analysis. DNA examination is carried out in forensics for the study of biological material. With the help of this study, forensics can detect traces of an intruder or victim on objects or bodies.
Genetic expertise is based on a comparative analysis of markers in biological samples of people, which gives us information about the presence or absence of relationship between them. Each person has a unique "genetic passport" - this is his DNA, which stores complete information.
The forensic medical examination uses a high-precision method called fingerprinting. It was invented in the UK in 1984 and is a study of samples of biological samples: saliva, semen, hair, epithelium or body fluids in order to identify traces of a criminal in them. Thus, the DNA forensic examination is designed to investigate the guilt or innocence of a certain person in unlawful acts, to clarify cases of doubtful motherhood or paternity.
In the sixties of the last century, German specialists organized a society to promote genome research in the judicial and legal sphere. By the early nineties createda special commission that publishes important works and discoveries in this area, being the legislator of standards in the work of forensic examination. In 1991, this organization was given the name "International Society of Forensic Geneticists". Today, it consists of more than a thousand employees and 60 global companies that are engaged in research in the field of judicial proceedings: serology, molecular genetics, mathematics, biostatics. This has brought uniform high standards to the world forensic practice, which improve the detection of crimes. DNA forensic examination is carried out in specialized laboratories that are part of the complex of the judicial and legal system of the state.
Problems of forensic genomic analysis
The main task of forensic experts is to examine the submitted samples and make a DNA conclusion, according to which it is possible to determine the biological "imprints" of a person or establish a blood relationship.
DNA samples can be contained in the following biological materials:
- sweat marks;
- pieces of biological tissues (skin, nails, muscles, bones);
- body fluids (sweat, blood, semen, transcellular fluid, etc.);
- hair (must have hair follicles).
For a forensic medical examination, a specialist is presented with physical evidence from the crime scene containing genetic material and evidence.
Currently, a database of criminal DNA is being created in a number of progressive countries. This improves disclosurecrimes even with expired statute of limitations. The DNA molecule can be stored for many centuries without change. Also, the information will be very useful for identifying a person in case of mass death of people.
Legislative framework and prospects for DNA forensics
In Russia in 2009, the law "On mandatory genomic fixation" was adopted. This procedure is carried out for prisoners, as well as for people whose identity has not been established. Citizens who are not included in this list take the test voluntarily. What can such a genetic base give:
- reduce atrocities and reduce crime;
- may become the main evidentiary fact in solving a crime;
- solve the problem of inheritance in controversial cases;
- to establish the truth in matters of fatherhood and motherhood.
DNA conclusion can also provide interesting information about a person's personality: genetic predisposition to diseases and addictions, as well as propensity to commit crimes. An amazing fact: scientists have discovered a certain gene that is responsible for a person's propensity to commit atrocities.
DNA expertise in forensic science has helped solve more than 15,000 crimes worldwide. It is especially fascinating that it is possible to solve a criminal case only by a hair or a piece of the criminal's skin. The creation of such a base prophesies great prospects not only in the judicial sphere, but also in such industries as medicine and pharmaceuticals. DNA research helps to cope with intractable diseases that are inherited.
Procedureperforming DNA analysis. Establishing paternity (maternity)
Currently, there are many private and public accredited laboratories where DNA testing can be done. This examination is based on a comparison of DNA fragments (loci) in two samples: the intended parent and the child. Logically, a child receives 50% of its genes from its parents. This explains the similarity to mom and dad. If we compare a certain section of the child's DNA with a similar section of the DNA of the intended parent, then they will be the same with a probability of 50%, that is, 6 out of 12 loci will coincide. %. If only one of the twelve loci matches, this probability is minimized. There are many accredited laboratories where DNA testing can be done privately.
The accuracy of the analysis is affected by the nature and number of loci taken for the study. DNA studies have shown that the genetic material of all people on the planet matches 99%. If we take these similar sections of DNA for analysis, it may turn out that, for example, an Australian aborigine and an Englishwoman will be absolutely identical personalities. Therefore, for an accurate study, areas unique to each individual are taken. The more such areas will be subjected to research, the higher the probability of accuracy of the analysis. For example, with the most thorough and high-quality study of 16 STRs, the conclusionDNA will be obtained with an accuracy of 99.9999% when confirming the probability of maternity / paternity and 100% when refuting the fact.
Establishing a close relationship (grandmother, grandfather, niece, nephew, aunt, uncle)
DNA analysis for relationship is not fundamentally different from the test for paternity and motherhood. The difference is that the amount of total genetic information will be half that of a paternity test, and will be approximately 25% if 3 out of 12 loci match exactly. In addition, the condition must also be observed that the relatives between whom kinship is established belong to the same line (by mother or father). It is important that the transcript of the DNA analysis is as reliable as possible.
Establishing DNA similarities between siblings and half-siblings
Siblings and brothers receive one set of genes from their parents, so DNA testing reveals 75-99% of the same genes (in the case of identical twins, 100%). Half-siblings can only have a maximum of 50% of the same genes and only those that are passed down through the maternal line. A DNA test can show with 100% accuracy whether siblings are siblings or stepbrothers.
DNA test for twins
Twins by nature of biological origin are identical (homozygous) or dizygotic (heterozygous). Homozygous twins develop from one fertilized cell, are of only one sex and are completely identical in genotype. Heterozygous is formed from different fertilizedeggs, are of different sexes and have small differences in DNA. Genetic testing is able to determine with 100% accuracy whether twins are monozygous or heterozygous.
Y chromosome DNA testing
The transmission of the Y-chromosome occurs from father to son. With the help of this type of analysis, it is possible to determine with high accuracy whether men are members of the same family and how close they are related. Y-chromosome DNA determination is often used to create a family tree.
Mitochondrial DNA analysis
MtDNA is inherited through the maternal line. Therefore, this type of survey is very informative for tracing kinship through the mother's side. Scientists use mtDNA analysis to control evolutionary and migratory processes, as well as to identify people. The structure of mtDNA is such that two hypervariable regions HRV1 and HRV2 can be distinguished in it. By conducting research on the HRV1 locus and comparing it with the Standard Cambridge Sequence, you can get a DNA conclusion about whether the people under study are relatives, whether they belong to the same ethnic group, the same nationality, the same maternal line.
Deciphering genetic information
In total, a person has about a hundred thousand genes. They are encoded into a sequence that consists of three billion letters. As mentioned earlier, DNA has the structure of a double helix, interconnected through a chemical bond. The genetic code consists of numerous variations of five nucleotides, designated: A (adenine), C(cytosine), T (thymine), G (guanine) and U (uracil). The order of localization of nucleotides in DNA determines the sequence of amino acids in a protein molecule.
Scientists have discovered a curious fact that about 90% of the DNA chain is a kind of genetic slag that does not carry important information about the human genome. The remaining 10% are broken down into their own genes and regulatory regions.
There are times when DNA chain doubling (replication) fails. Such processes lead to the appearance of mutations. Even a minimal error of one nucleotide can cause the development of a hereditary disease that can be fatal to humans. In total, scientists know about 4,000 such disorders. The danger of the disease depends on which part of the DNA chain the mutation will affect. If this is an area of genetic slag, then the error may go unnoticed. This will not affect normal operation. If a replication failure occurs at an important genetic segment, then such an error can cost a person his life. DNA research from this position will help geneticists find a way to prevent gene mutation and defeat hereditary diseases.
The DNA Genetic Code Table helps genetic scientists to add up complete information about the human genome.
| Amino acid | mRNA codons |
|
Arginic acid Lysine Isoleucine Alanine Arginine Leucine Glycine Tryptophan Methionine Glutamine Valine Cysteine Proline Aspartic acid Serine Histidine Asparagine Threonine Tyrosine |
TsGU, TsGTS, TsGG, TsGA AAG, AAA CUG, UCA, AUU, AUA, UAC GCC, GCG, GCU, GCA AGG, AHA UUG, CUU, UUA, CUU CAG, CAA UGG AUG GAG, GAA GUTS, GUG, GUU, GUA UHC, UGU CC, CCG, CCU, CCA GAC, GAU UCC, UCG, UCU, UCA CAC, CAU AAC, AAU ACC, ACG, ACC, ACA UAV, UAU |
Genetic screening during planning and during pregnancy
Genetic scientists recommend that couples undergo genetic research at the stage of offspring planning. In this case, you can find out in advance about possible changes in the body, assess the risks of having children with pathologies and determine the presence of genetically inherited diseases. But practice shows that DNA studies of women most often take place when they are pregnant. Under such circumstances, information will also be obtained on the likelihood of malformations in the fetus.
Genetic screening is voluntary. But there are a number of reasons why a woman must undergo such a study. These readings include:
- biological age over 35;
- hereditary maternal diseases;
- history of miscarriages and stillbirthschildren;
- presence of mutagenic factors during conception: radioactive and X-ray radiation, the presence of alcohol and drug addiction in parents;
- previously born children with developmental pathologies;
- viral diseases transmitted by a pregnant woman (especially rubella, toxoplasmosis and influenza);
- ultrasound indications.
A blood test for DNA will most likely determine the predisposition of the unborn baby to diseases of the heart and blood vessels, bones, lungs, gastrointestinal tract and endocrine system. This study also shows the risk of having a baby with Down and Edwards syndromes. The DNA report will give the doctor a complete picture of the condition of the woman and child and will allow them to prescribe the correct corrective treatment.
Methods of genetic research during pregnancy
Traditional research methods include ultrasound and a biochemical blood test, they do not pose any danger to the woman and the fetus. This is the so-called screening of pregnant women, carried out in two stages. The first is carried out at a gestational age of 12-14 weeks and allows you to identify serious fetal disorders. The second stage is carried out at 20-24 weeks and provides information about minor pathologies that may occur in the baby. If there is evidence or doubt, doctors may prescribe invasive methods of analysis:
- Amniocentesis or amniotic fluid sampling for research. A puncture is made in the uterus with a special needle, the necessary amount of amniotic fluid is collected foranalysis. This manipulation is carried out under ultrasound control to avoid injury.
- Chorion biopsy - placenta cell sampling.
- Pregnant women who have had an infection are prescribed placentogenesis. This is a rather serious operation and is carried out starting from the twentieth week of pregnancy, under general anesthesia;
- Umbilical cord blood sampling and analysis, or cordocentesis. It can only be done after the 18th week of pregnancy
Thus, it is possible to find out from genetic analysis how your child will be, long before his birth.
Cost of DNA testing
A simple layman who does not encounter this procedure, after reading this article, a reasonable question arises: "How much does a DNA examination cost?". It is worth noting that the price of this procedure depends on the chosen profile of the study. Here is the approximate cost of a DNA test:
- paternity (motherhood) – 23000 rubles;
- close relationship - 39000 rubles;
- cousin - 41,000 rubles;
- establishment of a sibling/half-brother (sister) – 36,000 rubles;
- twin test - 21000 rubles;
- for the Y-chromosome - 14,000 rubles;
- for mtDNA - 15000 rubles;
- consultations on establishing kinship: oral - 700 rubles, written - 1400 rubles
In recent years, scientists have made many great discoveries that are redefining the postulates of the scientific world. DNA research is ongoing. Scientists are driven by a great desire to discover the secret of the human genetic code. Much has already been discovered and explored, but how much of the unknown lies ahead! Progress is not worth itin place, and DNA technology is firmly embedded in the life of every person. Further research of this mysterious and unique structure, which is fraught with many secrets, will reveal to mankind a huge number of new facts.
