In this section:
Transgenesis
Molecular biology encompasses the isolation of individual genes or gene families which may be used in 'gene therapy'-style approached to livestock. Isolated genes can be used to enhance cellular porcesses that are known in impinge upon production traits (in quantitative or qualitative ways) or to add novel functions to cells and tissues. In the preceeding years, SARDI has used this method and sheep wool keratin genes to modify wool fibre properties in sheep. This approach, known as transgenesis, involves transferring genes know as transgenes.
In one method (pronuclear microinjection) a transgene is injected into a livestock embryo at the single-cell stage and becomes inserted into one of the chromosomes. When this cell divides, the transgene is copied with the rest of the chromosomal DNA such that as the embryo develops to full-term, each cell in the animal born has the transgene.
In another method (somatic cell nuclear transfer, or 'cloning', as used recently to produce the sheep Matilda) a gene is first transferred into the chromosomes of a cell in culture then that cell's nucleus is used to replace the nucleus on an oocyte. During subsequent development in culture, then in utero and at term, this animal also carries the extra gene.
In both methods, a transgenic animal is made.
When single genes are transferred to embryos (more than one can be used) the genetic alteration to the resulting animal is quite precise: only a single gene is changed while all other genes in the chromosomes are generally unaltered. (The latter 'cloning' methodology is preferred as it allows the chromosomal insertion point of the transgene to be controlled.) In this way, the genetics of a valuable animal may be preserved and added to in a defined manner, so that the effects of transgenes and their expression can be accurately assessed. In the case of sheep wool, transgenesis provides an opportunity to develop wools with different protein compositions and properties that could be an advantage during processing or which might provide novel qualities to the end product. We are awaiting new funding to produce more transgenic sheep, which carry new transgenes designed to modify wool properties and to promote wool growth.
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