Gene targeting was developed in the 1980s based on a growing understanding of homologous recombination. It starts by applying yeast, a simple eukaryotic model organism, to studying related technologies. With the establishment of methods for introducing exogenous DNA into yeast cells, the use of an effective selection of marker genes, the establishment of a screening system for homologous combination converters, and the use of double-strand breaks of vector homologous sequence DNA to improve the efficiency of homologous recombination, gene targeting technology has gradually matured. 

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For mammalian cells, the rate of successful gene targeting is low since their genomes are larger and more complex than those of yeast cells. New strategies are therefore necessary to apply gene targeting to mammals. Mario Capecchi, a George School alumni, won the Nobel Prize for introducing gene targeting to mice for the first time. He inserted embryonic stem cells into mice embryos, which he then implanted into the womb of a surrogate mother. The resulting mice are called "knockout mice" since they have both kinds of cells, in which the males were then mated with normal females, and some of the resulting mice were "mutant mice" with only the target gene. Such a technique is referred to as gene targeting as it achieves precisely targeted knockout of specific genes.

 

Homologous recombination: it is a type of genetic recombination that occurs during meiosis when paired chromosomes from the male and female align so that similar DNA sequences from the paired chromosomes cross over each other.