Gene targeting

Gene targeting係遺傳學嘅一種技術，用同源重組(homologous recombination) 來改隻内源性基因(endogenous gene)。呢種技術可用來刪走一隻基因、拎走外顯子(:en:exons) 同埋引入點突變(:en:point mutations)。Gene targeting 可以係 permanent 或者係條件性(conditional) 嘅。「條件」可以係隻生物發育/生存中嘅 一段時間，或者限定喺某種組織。搞基因 targeting，要幫每一有關嘅基因整出一特定嘅vector。但係，佢可以用響任一基因，唔使理啲轉錄(transcriptional)活動同埋基因嘅大細。

點做 

Gene targeting methods vary depending on organism. To target genes in mice a rough outline of the necessary steps is as follows: First, a targeting construct made out of DNA is generated in bacteria. It typically contains part of the gene to be targeted, a reporter gene, and a selectable marker. This construct is then inserted into mouse embryonic stem cells in culture. After cells with the correct insertion have been selected, they can be used to contribute to a mouse's tissue via embryo injection. Finally, chimeric mice where the modified cells made up the reproductive organs are selected for via breeding. After this step the entire body of the mouse is based on the previously selected embryonic stem cell.

同 gene trapping 比 

Gene trapping is based on random insertion of a trap cassette while gene targeting targets a specific gene. Trap cassettes can be used for many different genes while the flanking homology regions of gene targeting cassettes need to be adapted for each gene. This makes gene trapping more easily amenable for large scale projects than targeting. On the other hand, gene targeting can be used for genes with low transcriptions that would go undetected in a trap screen.  Also, the probability of trapping increases with intron size. For gene targeting these compact genes are just as easily altered.

2007年諾貝爾獎 
Mario R. Capecchi,  Martin J. Evans and Oliver Smithies were declared winners of the 2007 Nobel Prize in Physiology or Medicine for their work on "principles for introducing specific gene modifications in mice by the use of embryonic stem cells", or gene targeting.

參攷

genetics, genetic engineering
 gene knockout, knockout mouse
 gene trapping (random gene knockout technique)
 gene knockdown (reduction not removal of a gene product)
 Mus musculus (house mouse; common model organism)
 Toll-like receptor (example of a gene targeted for analysis)

guide to gene targeting by the University of California, San Diego
 outline of gene targeting by the University of Michigan
 gene targeting diagram & summary by Heydari lab, Wayne State University

分子生物學
遺傳工程
生物工程
基因改造生物