Whose son is this child?

Aiming at this problem, the following scheme is given:

Brief introduction of DNA paternity: DNA identification

DNA typing is the most commonly used method to identify parent-child relationship. Human blood, hair, saliva, oral cells and bones can all be used for paternity testing, which is very convenient.

Detection principle

The principle of ABO blood group identification is to classify blood groups into four types: A, B, AB and O according to whether there is A antigen or/and B antigen on red blood cells. ABO blood group can be accurately identified by erythrocyte agglutination test and positive (serum test) and negative (cell test) typing. The so-called positive typing is to determine whether there is corresponding A antigen or/and B antigen on red blood cells with known anti-A and anti-B typing serum, and the so-called reverse typing is to determine whether there is corresponding anti-A or anti-B antigen in serum with known A cells and B cells. Parents: Type A+Type A, the offspring may be Type A and Type O, but the offspring may not be Type B and AB.

Parent: type B+type A, the offspring may be type A, type B, type AB and type O, and the offspring may not be: none.

Parents: type B+type B, the offspring may be type B or O, but the offspring may not be type A or AB.

Parental: one or both of them are AB type, and the offspring may be A type, B type and AB type, but the offspring may not be O type.

Parent: type A +O, the offspring may be type A or O, but the offspring may not be type B or AB.

Parents: type B +O, the offspring may be type B and O, and the offspring may not be type A and AB.

Parents: O type +O type, the offspring may be O type, and the offspring may not be A type, B type or AB type.

Identification method DNA fingerprint

Dna fingerprinting refers to DNA polymorphism with complete individual specificity, and its individual recognition ability is comparable to that of finger fingerprints, hence the name. It can be used for personal identification and paternity test, and hybridize with the restricted fragment of human nuclear DNA to obtain hybridization bands with different lengths composed of alleles at multiple sites. This pattern is rarely exactly the same as two people, so it is called "DNA fingerprint".

Because DNA fingerprint has high variability and stable heredity, and it is still inherited in a simple Mendelian way, it has become the most attractive genetic marker at present and can be widely used in paternity testing.

Features: 1. High specificity: the research shows that the probability of two random individuals having the same DNA pattern is only 3×10-11; If two probes are used for comparison at the same time, the probability of two individuals being the same is less than 5× 10- 19. The world population is about 5 billion, that is, 5× 10 9. Therefore, unless they are identical twins, it is almost impossible for two people to have the same DNA fingerprint. 2. Stable inheritance: DNA is the genetic material of human beings, and its characteristics are inherited by parents. It is found that almost every band in DNA fingerprint can be found in the atlas of one of its parents, which conforms to the classical Mendelian inheritance law, that is, 50% of the characteristics of both sides are passed on to future generations on average. 3. Somatic cell stability: that is, the DNA fingerprints produced by different tissues such as blood, muscle, hair and semen of the same person are completely consistent.

STR detection

Short tandem repeat (STR), also known as microsatellite DNA, is a kind of DNA polymorphism site widely existing in human genome. It is composed of 2~6 base pairs in series and arranged repeatedly. The length of STR loci is generally between100 and 300 BP. Because of the differences of DNA fragment length or DNA sequence among individuals, it is highly polymorphic, and it follows Mendel's dominant pattern in gene transmission. Because of its short gene fragment, high amplification efficiency and accurate typing, it is called the second generation DNA fingerprint and has been widely used in paternity testing in recent years.

Scottish national party

SNP has become the third generation genetic marker, and many phenotypic differences and susceptibility to drugs or diseases may be related to SNP.

RFLP analysis

The recombination frequency of restriction map markers and visible phenotype is measurable, and the genetic map is divided into two molecular markers: genotype and phenotype. Restriction markers have become a powerful tool to determine genetic genes at the molecular level, because they are not affected by genomic changes that have an impact on phenotype.

Rflp and snp are the basis of linkage map, which is of great significance to paternity test. We can know its position in many genetic disease gene maps that cause human diseases, but we don't know its corresponding gene sequence or protein. For example, cystic fibrosis conforms to Mendel's genetic law, but the molecular properties of its mutant are unknown before the gene is labeled. When comparing the dna restriction maps of patients and normal people, we often find that specific restriction sites appear or are missing in their genomes. If the restriction marker is linked to the phenotypic feature, the restriction site is located near the phenotypic feature gene. It has been identified that this marker has the following two meanings: (1) It provides a procedure for diagnosing diseases; It provides a reference for gene isolation.

Snp appears frequently in human genome, which is helpful to draw genetic map. We can infer from the number of SNPs that there is one SNP for every 1000 to 2000 bases in the human genome. For the identification of genetic disease genes, we can quickly locate them through the recent snp.

Similarly, when rflp is applied to genetic mapping, we can detect the relationship between unknown loci and polymorphic fragments to locate.

The appearance of rflp provides a basis for accurate paternity testing technology. By comparing the rflp maps of parents and children at appropriate positions, we can accurately judge their genetic relationship.

DNA paternity steps are as follows:

Step 1: DNA extraction

The DNA contained in the sample nucleus is extracted and then purified to remove impurities in the sample.

Step 2: PCR amplification

The Chinese name of PCR is polymerase chain reaction. Simply put, the step of PCR amplification is to copy a large number of fragments we need on the PCR instrument through enzymatic reaction and enlarge them to the extent that some special instruments can see them.

Step 3: Post-PCR reaction

This step is mainly the preparation stage of sequencing instrument detection, which opens the double-stranded DNA and adds some internal standards for detection, mainly marking the length of the detection fragment.

Step 4: Capillary sequencer detection.

Because DNA is charged, capillary electrophoresis has different electrophoresis speeds for different fragments of DNA. Under the same voltage and electrophoresis time, the swimming distance is different. These different distances can be distinguished by the internal standard measurement added in the early stage, and displayed on the computer through certain software, which is convenient for inspectors to process and analyze the data.

Step 5: Analyze the data and issue a report.

It is mainly for inspectors to analyze, summarize and calculate the obtained results, and then make appraisal conclusions and reports.