=TRANSGENESIS - Vectors= Transgenesis is the process of introducing a gene from another organism (transgene) into another living organism so that the organism will express a new trait or pass the trait onto its offspring. Transgenesis can be split into two categories. Using a '''''virus''''' to introduce a transgene into a cell is also called '''''transduction'''''. Using a '''''non-viral method''''' of introducing a transgene into a cell is also called '''''transfection'''''. In order to transfer a gene into eukaryote cells such as animal and plant cells a vector is required. This is because eukaryote cells are not capable of taking up foreign DNA into the nucleus. A vector is simply a method of getting the transgene into the nucleus of a cell from the target organism. Vectors can also be used to make to make transgenic organisms that produce valuable protein based products such as insulin. They can also also to introduce novel (new) characteristics to an organism. For example, genes that code for pest resistance might be incorporated into a plant species in order to increase the quality and yield of a given crop. The same idea can be applied to humans; faulty disease causing genes could be replaced with normal functioning genes (this is referred to as gene therapy). [image:] '''Chemical''' Copies of the transgene can be mixed with various chemicals that promote their uptake into the cell. One good example is the use of '''liposomes''' - small, membrane-bounded bodies made of phospholipids. Liposomes are essentially and artificial vesicle that can fuse with the cell membrane, releasing the DNA into the cell. [image:] '''Electroporation''' Exposing cells to short pulses of electricity increases their permeability allowing some uptake of DNA fragments. High intensity ultrasound also has a similar effect (called sonoporation) [image:] '''Pro-nuclear Injection''' Genetic material can also be injected directly into the nucleus of another cell using a very fine needle (micro-injection). Multiple copies of the transgene are injected into a recently fertilised egg cell which is then transferred into the uterus of a surrogate mother. [image:] '''Gene Gun''' Microscopic metal beads are soaked in a solution containing many copies of the transgene. They are then fired directly into the target cells, delivering the transgene into the cell. [image:] '''Viral Vectors''' Virsues naturallyinsert their DNA into host cells. The host cell normally expresses the viral genes, which code for the production of of more viral proteins. If the viral genes are replaced with a trangene the virus will deliver this into the cell without causing an infection. [image:] '''Plasmid Vectors''' Plasmids are naturally occurring loops of DNA found within many species of bacteria. Normally these plasmids are only passed between closely related bacterial species, however, one species (''Agrobacterium tumefaciens'') can insert it's plasmid into plant cells. A transgene can be added to the plasmid and delivered into the plant cell. ==Low Success Rates== Most of these techniques only produce a very small percentage of cells that express the transgene. In order for the gene to be expressed it must make it's way into the nucleus. For it to be passed on during cell division (mitosis and meiosis) it must integrate into the target cells genome (usually by recombination - crossing over).
Credit: Ben Himme