转基因 z-bo 2020-08-14 477

　　1. High production efficiency

　　Traditional transgenic technologies such as microinjection are random and invisible. The copy number and integration sites of foreign genes are random, and mosaicism may occur, the integration rate is extremely low, and the number of transgenic animals obtained is smaller. According to statistics, some medical companies used microinjection technology to produce transgenic animals on average from 1989 to 1997 to obtain an average of 51.4 animals to obtain a transgenic offspring, while obtaining a transgenic cloned offspring requires only 20.8 mothers.

　　2. Short cycle and low cost

　　Through nuclear transfer cloning, a large number of homogenous transgenic cloned animals can be produced quickly. In theory, transgenic cloning technology can produce a complete transgenic cloned animal line in only one generation, thus saving time and cost. They are all genetically modified embryos, thus improving production efficiency and reducing costs.

　　3, can determine the sex of offspring

　　Transgenic cloned animals for the purpose of biopharmaceuticals, gender is very important in production, for example, females are required to produce milk. If the first generation is male, you will have to wait until the daughter is mature before giving birth, at least two generations. Since somatic cells are selected as the donor, the sex can be determined in advance, and the sex can also be detected by PCR, and only cells with the right sex are selected as the nuclear donor.

　　The key technology of animal genetic modification

　　The main technical steps of transgenic animals include: isolation and cloning of target genes; construction of expression vectors; acquisition of recipient cells; gene introduction; selection of recipient animals and transfer of transgenic embryos; detection of transgene integrated expression; performance of transgenic animals Observation and separation and purification of transgenic expression products; genetic performance research and performance selection of transgenic animals; formation of new groups of transgenic animals, etc.

　　1. Microinjection

　　The operation steps include the preparation of the target gene, the preparation of mice, the separation of fertilized eggs, microinjection, the transplantation of fertilized eggs, and the identification of transgenic mice.

　　2. Retroviral method

　　The nucleic acid of a retrovirus is a single-stranded RNA molecule, and its gene consists of two parts. One is a cis-acting sequence, which is necessary for virus replication and integration; the other is a trans-acting sequence, which encodes the virus's packaging protein. The trans-acting sequence is replaced by the foreign gene to construct the recombinant DNA.

　　In addition, the packaging protein gene is introduced into specialized cells and integrated into the chromosomes to form packaging cells. If recombinant viral DNA is introduced into such packaging cells, the viral packaging protein can package the DNA into infectious recombinant protein particles, and can infect animal cells to introduce recombinant DNA into host cells. This method is currently the most effective and successful method for preparing transgenic chickens.

　　3. Embryonic stem cell method

　　Embryonic stem cells are undifferentiated cells in the blastocyst at the early stage of mammalian embryonic development. Blastocysts contain inner cell populations, and these undifferentiated cells can further divide, differentiate, and develop into individuals. Since the inner cell population can develop into a complete individual, these cells are considered to be pluripotent. When the inner cell population is cultured in a petri dish, we call it embryonic stem cells. The specific process of using this method to produce transgenic animals is as follows: Isolate embryonic cells from 3.5-day-old pregnant mice, transfer them to a petri dish and culture for a period of time, separate the inner cell mass and collect stem cell clones, and then dissolve the cells by enzymatic treatment for stem cell culture , Transfection, and finally implantation in surrogate mother mice.

　　In addition, the gene targeting technology is an experimental method to change the genetic information of living organisms. Its production and development are based on the achievements of embryonic stem (ES) cell technology and homologous recombination technology, and promote the development of related technologies. Further development. Through targeted modification of the genetic information of living organisms, including gene inactivation, introduction of point mutations, deletion mutations, introduction of foreign genes, deletion of large fragments of chromosomes, etc., the modified genetic information can be inherited in vivo and express mutations. Traits, so that major issues in life sciences such as gene function can be studied, and related disease treatments, new drug screening and evaluation models can be provided. The development of gene targeting technology has made it possible to modify the genetic material of specific cells, tissues or individual animals.

　　Four, sperm carrier method

　　Sperm vector method is when sperm and foreign DNA are mixed culture, the foreign DNA can directly enter the sperm head, and the foreign gene is introduced into animal cells through fertilization. The methods of introducing foreign DNA into sperm cells include DNA and sperm co-incubation method, electroporation method, and liposome transfection method.

　　5. Somatic cell nuclear transfer

　　In 1997, British scientists Schnieke and Wilmut successfully cloned "Dolly" through somatic cell nuclear transfer technology. In June 1997, Wilmut reported that embryonic cells were used as nuclear donors to obtain a transgenic sheep "Polly" that expresses coagulation factor IX for the treatment of human hemophilia. In 1999, American scientist Alexander cloned three goats and changed their genetic traits so that their milk contained a protein that has a curative effect on heart disease.

　　6. Receptor-mediated method

　　is to link the foreign DNA with the receptor molecule and then co-culture with embryonic cells. The receptor can mediate the foreign DNA into the recipient cell to achieve gene transfer. In 1999, Ivanava used the receptor-mediated method to make transgenic mice.