#1 Embryo technology in laboratory animals
Recent progress in genetics has been in part due to progress in embryo technology, as new developments in embryology have made increasingly sophisticated genetic manipulations possible. Although post-implantation embryos may in some
cases be used as experimental subjects. most procedures make use of pre-implantation stages. Techniques such as in Vitro culture and fertilisation of embryos, embryo transfer and the cryopreservation of gametes and embryos are now routine
in many laboratories. and play an important part in the creation of genetically manipulated animals. The production of chimaeras has also become routine. Aggregation chimaeras have been made for some years‘ while injection chimaeras (created by the injection of embryonic stem cells or blastomeres into the blastocyst cavity) play an important part in the production of mice with alterations o specific genes (the process of "gene targeting").The techniques of embryo cloning and
embryo biopsy have also found practical applications in animal production and medicine. But one of the most significant advances in embryo technology has been the development of embryonic stem cells (ES cells), lines of cultured cells that
can, when introduced into a host blastocyst, participate in the formation of all tissues. Animals can thus be produced carrying genetic alterations induced in ES cells. Although at present ES cells are available for only a few strains of mice, it is expected that in the future ES cell lines from other species will be developed.