Our world is inhabited by a variety of organisms: from microscopic, visible only through a powerful microscope, to huge ones, whose weight reaches several tons. Despite this 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. An exception can only be identical twins. What makes each organism living on our planet so unique?
Each cell has a central organ - this is the nucleus. It contains some material units - genes located on the chromosomes. From a chemical point of view, genes are deoxyribonucleic acid, or DNA. This macromolecule, curled in a double helix, is responsible for the inheritance of many traits. Thus, the meaning of DNA is the transfer of genetic information from parents to descendants. To deduce this truth, scientists all over the world for two centuries have set up incredible experiments, put forth bold hypotheses, failed and experienced triumph from great discoveries. It is thanks to the work of great researchers and scientists that we today know what DNA means.
By the end of the 19th century, Mendel established the basic laws of the transfer of attributes 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 in 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 discovered. In the forties, scientists Boris Efrussi, Edward Tatum and George Beadle expressed a bold hypothesis that genes produce proteins, that is, they store special information on 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 a genetic code and deduced the 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. 20 amino acids and 4 nucleotides are involved in the formation of proteins.
There are two types of nucleic acids: DNA (deoxyribonucleic acid) and RNA (ribonucleic acid). Their structure is similar in that both substances have a nucleotide in their composition: nitrogenous base, phosphoric acid residue and carbohydrate. But the difference is that DNA has deoxyribose and RNA has ribose. Nitrogen bases are purine and pyrimidine. The DNA contains purine adenine and guanine and pyrimidine thymine and cytosine. RNA includes in its structure the same purines and pyrimidine cytosines and uracil. By combining the phosphoric acid residue of one nucleotide and the carbohydrate of another, a skeleton of a polynucleotide is formed to which nitrogenous bases cling. Thus, quite a lot of different compounds can be obtained that determine species diversity.
The DNA molecule is a double helix of two large polynucleotide chains. They are linked by purine of one chain and pyrimidine of the other. These connections are not accidental. They obey the law of complementarity: bonds are capable of forming between themselves adenyl nucleotide with thymyl, guanilic with cytosyl, since they complement each other. This principle gives the DNA molecule a unique property of self-reproduction. Special proteins - enzymes - move and break the hydrogen bonds between the nitrogenous bases of both chains. As a result, two free nucleotide chains are formed, which are completed by the available free nucleotides 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 maternal.
Genetic code and its secrets
DNA research allows you to understand the individuality of each organism. This can be easily imagined from an example of tissue incompatibility in organ transplants from a donor to a recipient. A āforeignā organ, for example, donor skin, is perceived by the recipient organism as hostile. This triggers the immune response chain, 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 emerged 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 experimentally. The bacteriologist F. Griffiths conducted an interesting experiment with pneumococci. He introduced a dose of the pathogen to mice. The vaccines were of two types: form A with a capsule of polysaccharides and form B, deprived of the capsule, both are inherited. The first species was destroyed thermally, while the second did not pose any danger to mice. What was the surprise of the bacteriologist when all the mice died of pneumococci form A. Then the reasonable question arose in the scientistās head about how the genetic material was transmitted - through protein, polysaccharide or DNA? After almost twenty years, the American scientist Oswald Theodor Avery was able to answer this question. He set up a series of experiments of an exclusive nature and found that inheritance continues when protein and polysaccharide are destroyed. The transmission 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.
The disclosure of the structure of DNA and the genetic code has allowed humanity to take a tremendous step forward in the development of such fields of activity as medicine, forensic science, industry and agriculture.
Forensic DNA analysis
Currently, progressive criminal and civil proceedings are 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 attacker or injured person on objects or bodies.
Genetic examination is based on a comparative analysis of markers of biological samples of people, which gives us information about the presence or absence of a relationship between them. Each person has a unique āgenetic passportā - this is his DNA, which stores complete information.
In forensic science, a high-precision method called fingerprinting is used. It was invented in the UK in 1984, is a study of samples of biological samples: saliva, sperm, hair, epithelium or body fluids in order to identify traces of a criminal in them. Thus, forensic DNA 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 experts organized a society to promote genome research in the legal field. By the beginning of the nineties, a special commission was created, which is engaged in the publication of important works and discoveries in this area, being the legislator of standards in the conduct of forensic examination. In 1991, the organization was given the name "International Society of Forensic Genetics." Today, it consists of more than a thousand employees and 60 global companies that are engaged in research in the field of judicial production: serology, molecular genetics, mathematics, biostatics. This has brought uniform high standards to the world forensic practice that improve crime detection. DNA forensics is performed in specialized laboratories, which are part of the state judicial system.
Forensic Genomic Tasks
The main task of forensic experts is to examine the submitted samples and make a DNA conclusion, judging by which it is possible to determine the biological āimprintsā of a person or establish blood relationship.
DNA samples can be contained in the following biological materials:
- traces of sweat;
- pieces of biological tissue (skin, nails, muscles, bones);
- body fluids (sweat, blood, sperm, transcellular fluid, etc.);
- hair (hair follicles are required).
To conduct a forensic examination, a specialist is presented with material evidence from the crime scene containing genetic material and evidence.
Currently, a number of progressive countries are creating a DNA database of criminals. This allows to increase the detection of crimes even with the expired statute of limitations. A DNA molecule can be stored for many centuries without change. Also, the information will be very useful for identifying a person during mass deaths.
Legislative basis and prospects of forensic DNA
In Russia in 2009, the law "On Compulsory Genomic Fixation" was adopted. Such a procedure is carried out for prisoners, as well as for people whose identity has not been established. Citizens who are not on this list voluntarily test. What can give such a genetic base:
- reduce the number of atrocities and reduce crime;
- can become the main evidence in solving a crime;
- solve the problem of inheritance in disputed cases;
- establish the truth in matters of fatherhood and motherhood.
Conclusion of DNA can also provide interesting information about a personās personality: a genetic predisposition to disease and dependence, as well as a tendency to commit crimes. An amazing fact: scientists have discovered a certain gene that is responsible for a personās tendency to commit atrocities.
DNA forensics in forensics has helped to solve more than 15 thousand crimes worldwide. It is especially fascinating that a criminal case can be opened only by a thread or a piece of the skin of a criminal. The creation of such a base predicts great prospects not only in the judicial sphere, but also in industries such as medicine and pharmaceuticals. DNA research helps to cope with inherited diseases that are inherited.
DNA analysis procedure. Establishment of paternity (motherhood)
Currently, there are many private and public accredited laboratories where DNA analysis can be done. This examination is based on a comparison of the fragmented parts of DNA (loci) in two samples: the alleged parent and the child. Logically, the child receives 50% of the genes from his parents. This explains the similarity to mom and dad. If we compare a certain section of a childās DNA with a similar section of the DNA of the intended parent, then they will be the same with a 50% probability, that is, out of 12 loci they will coincide 6. If such indicators are detected, the conclusion of the DNA examination guarantees the probability of biological paternity or motherhood at 99.99 % If only one of the twelve loci coincides, this probability is minimized. There are many accredited laboratories where you can do DNA analysis privately.
The accuracy of the analysis is affected by the nature and number of loci taken for study. DNA studies have shown that the genetic material of all people on the planet is 99% identical. If you take these similar sections of DNA for analysis, it may turn out that, for example, the Australian aborigine and the Englishwoman will be absolutely identical personalities. Therefore, for an exact study, sites that are unique to each individual are taken. The more such areas will be investigated, the higher the probability of the accuracy of the analysis. For example, with the most thorough and high-quality study of 16 STRs, DNA conclusion will be obtained with an accuracy of 99.9999% when confirming the probability of motherhood / fatherhood and 100% when refuting the fact.
Establishment of close kinship (grandmother, grandfather, niece, nephew, aunt, uncle)
DNA analysis for kinship does not fundamentally differ 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 of the 12 loci are completely identical. In addition, the condition must also be met that relatives between whom kinship is established belong to the same line (maternal or paternal). It is important that the decoding of the DNA analysis is as reliable as possible.
Establishing DNA similarities between siblings
Siblings and brothers receive one set of genes from their parents, so 75-99% of the same genes are found during DNA examination (in the case of identical twins - 100%). Stepbrothers and sisters can have a maximum of only 50% of the same genes, and only those that are transmitted along the maternal side. A DNA test with an accuracy of 100% is able to show whether siblings are siblings or stepbrothers.
DNA test for twins
Twins, by the nature of biological origin, are single-egg (homozygous) or double-egg (heterozygous). Homozygous twins develop from one fertilized cell, are of only one sex and are completely identical in genotype. Heterozygous ones are formed from different fertilized eggs, are heterosexual and have small differences in DNA. Genetic examination is able to determine with accuracy 100% whether the twins are monozygous or heterozygous.
Y chromosome DNA testing
Y-chromosome transmission occurs from father to son. Using this type of analysis, it is possible to determine with high accuracy whether men are members of the same family and how closely they are related. Determination of DNA by the Y chromosome is often used to create the family tree of the family.
Mitochondrial DNA Analysis
Inheritance of mtDNA occurs on the maternal side. Therefore, this type of examination is very informative for tracking the relationship through the mother. Scientists use mtDNA analysis to control evolutionary and migration processes, as well as to identify people. The structure of mtDNA is such that two hypervariable zones HRV1 and HRV2 can be distinguished in it. Conducting studies of the HRV1 locus and comparing it with the Standard Cambridge Sequence, one can obtain a DNA conclusion about whether the people under study are relatives, whether they belong to the same ethnic group, one nationality, and one maternal line.
Transcript of genetic information
In total, a person has about one hundred thousand genes. They are encoded in 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 malfunctions occur when doubling a DNA chain (replication) . Such processes lead to the appearance of mutations. Even a minimal error of one nucleotide can cause the development of a hereditary disease, which can be fatal to humans. In total, scientists know about 4000 of these disorders. The danger of the disease depends on which part of the DNA chain is affected by the mutation. If this is an area of āāgenetic slag, then the error may go unnoticed. This will not affect normal functioning. If replication failure occurs on an important genetic segment, then such an error can cost a person life. DNA research from this perspective will help geneticists find a way to prevent gene mutations and defeat inherited diseases.
The DNA genetic code table helps learned geneticists compile complete information about the human genome.
DNA genetic code table| Amino acid | MRNA codons |
Glycine Methionine Aspartic acid | , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , , |
Genetic screening during planning and during pregnancy
Genetic scientists recommend couples to undergo genetic research at the planning stage of offspring. In this case, you can know 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 fetal malformations.
Genetic screening is voluntary. But there are a number of reasons why a woman must undergo such a study. These indications include:
- biological age in excess of 35 years;
- maternal hereditary diseases;
- history of miscarriages and stillbirths ;
- the 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 suffered by a pregnant woman (especially rubella, toxoplasmosis and flu);
- indications revealed by ultrasound.
A blood test for DNA will with a high degree of probability determine the predisposition of the future 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. Conclusion of DNA will give the doctor a complete picture of the condition of the woman and the child and will allow you to prescribe the correct corrective treatment.
Pregnancy genetic research methods
Traditional research methods include ultrasound and a biochemical blood test, they do not pose any danger to a woman and a 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 in 20-24 weeks and gives information about minor pathologies that may occur in the baby. If there is evidence or doubt, doctors can prescribe invasive methods of analysis:
- Amniocentesis or amniotic fluid withdrawal for research. A special needle makes a puncture in the uterus, the required amount of amniotic fluid is collected for analysis. This manipulation is carried out under the supervision of ultrasound to avoid injuries.
- Chorionic biopsy - placenta cell sampling.
- Pregnant women who have had an infection are prescribed placentogenesis. This is a rather serious operation and is carried out since the twentieth week of pregnancy, under general anesthesia;
- 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 a genetic analysis what your baby will be, long before his birth.
DNA examination cost
After reading this article, a simple average man who does not encounter this procedure raises a reasonable question: āHow much does DNA examination cost?ā It is worth noting that the price of this procedure depends on the chosen research profile. Here is the approximate cost of a DNA test:
- fatherhood (motherhood) - 23000 p .;
- close relationship - 39,000 p .;
- cousin relationship - 41,000 p .;
- the establishment of a sibling / stepbrother (36);
- twins test - 21000 r .;
- on the Y-chromosome - 14000 r .;
- mtDNA - 15000 r .;
- kinship counseling: oral - 700 p., written - 1400 p.
In recent years, scientists have made many great discoveries that revise the postulates of the scientific world. DNA research is ongoing. Scientists are driven by the great thirst for knowing the secret of the human genetic code. Much has already been discovered and explored, but how much is unknown ahead! Progress does not stand still, and DNA technology is firmly embedded in the life of every person. Further studies of this mysterious and unique structure, which is fraught with many secrets, will reveal to mankind a huge number of new facts.