What is the DNA left by the suspect? The police extracted NDA. What does this mean? Is DNA a fingerprint?

Dna (deoxyribonucleic acid) generally refers to deoxyribonucleic acid.

It is an organic compound with complex molecular structure. As a component of chromosome, it exists in the nucleus. Its function is to store genetic information. DNA molecules are large and consist of nucleotides. Nitrogenous bases of nucleotides are adenine, guanine, cytosine and thymine.

Pentose is deoxyribose. In 1953, james dewey watson in the United States, Crick and Wilkins in the United Kingdom described the structure of DNA: it consists of a pair of polynucleotide chains coiled around a central axis that is the same as each other.

Sugar-phosphate chain is outside the spiral structure, and the base faces inside. Two polynucleotide chains are connected by hydrogen bonds between bases, forming a fairly stable combination.

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Molecular characteristics of DNA:

1, stability

The double helix structure of DNA molecules is relatively stable. This is because within the double helix structure of DNA molecules, two long deoxynucleotide chains are stably connected in parallel through base pairs formed by hydrogen bonds.

In addition, the longitudinal interaction between base pairs further strengthens the stability of DNA molecules. This vertical interaction between base pairs is called base stacking force.

It is caused by the interaction between π electrons of aromatic groups. At present, it is generally believed that base stacking force is the most important factor to stabilize DNA structure.

Furthermore, the ionic bond formed between negatively charged phosphate groups and positively charged cations outside the double helix can reduce the electrostatic repulsion between the double strands, thus stabilizing the DNA double helix structure to some extent.

2. Diversity

Due to the different number of base pairs and the ever-changing arrangement order of base pairs, DNA molecules are diverse. For example, a DNA molecule with 4 000 base pairs carries four kinds of genetic information, namely 10.

3. Characteristics

Different DNA molecules have different base pair sequences, so each DNA molecule has its own specific sequence, which contains specific genetic information, thus making DNA molecules specific.

Starting from 1987, China police applied DNA detection technology to investigate and solve crimes for the first time.

Because DNA fingerprinting provides abundant individual-specific genetic markers, it is of great significance in forensic identification.

In the application of criminal cases in forensic medicine, if it is determined that a person is a criminal suspect, the DNA of his blood sample or hair can be extracted to make DNA fingerprints, and then compared with the DNA fingerprints of blood, semen, saliva, sputum, hair, bones or other physical components left over from the crime scene.

If they are the same, the fingerprints match, which proves that the suspect is the criminal who committed the crime, and vice versa. Usually, the signature of the above fingerprint matching is called "matching".

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Application of paternity test Since jeffries and others first identified the mother-child relationship in an immigration dispute in 1985, DNA fingerprinting technology has been used for paternity test for nearly 10 years.

Representative reports are as follows: In the process of identifying an unknown corpse, experts successfully identified the nameless corpse by comparing the DNA extracted from the residual blood of the rotting corpse with the DNA of the presumed victim's parents. In the case that routine serological tests can't make a positive conclusion on parent-child relationship, DNA fingerprinting can easily make a conclusion.

The identification of the wreckage of air crash victims usually relies only on forensic medicine and routine serological tests, so it is difficult to distinguish all the wreckage of air crash victims. Therefore, when conventional means are not feasible, DNA fingerprinting technology is the best choice.

Racial and Gender Identification The research of the Central Research Bureau of the British Home Office shows that DNA fingerprinting technology can be used for racial identification to a great extent. It can detect polymorphic DNA fragments of whites and African blacks and their frequency of occurrence in a specific range, which is representative of species. Someone identified the sex of DNA degradation in the blood of 20 years old, and successfully distinguished people from animals.

Other applications to identify whether twins are fraternal twins or identical twins only need to compare their DNA fingerprints.