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Genetic Transfer As genetic constructs are made in vitro (i.e., in a Petri dish); they must be re-introduced into biological cells to use the internal machinery of these cells to produce multiple copies of the gene. Using this method, large amounts of protein can be produced and extracted. Re-introduction of the genetic construct in a cell can be accomplished using a variety of methods, described below, including transfection, microinjection, or nuclear transfer. Transfection Transfection re-introduces the genetic construct into a host cell by exposing the genetic construct and the cells to a chemical or electrical stimulus. This stimulus forms transient cellular pores on the membrane of the cell allowing the genetic construct to diffuse into the cell. This method is generally used for tissue culture systems. Cells containing the genetic construct are selected and replicated forming multiple copies of the gene and, subsequently, of the protein. Microinjection Microinjection is a process whereby the genetic construct is literally injected into the pronucleus of a single-celled fertilized egg under the microscope using a fine glass needle. In 1-10% of the eggs, the genetic construct will integrate itself stably into the host genome. The egg is placed into a foster recipient and a normal pregnancy ensues. Microinjection is one of the traditional methods used by Nexia in its production of specific proteins in transgenic goats. Nexia's goats express the protein in mammary tissue so that it can be collected easily in the goat's milk. Nuclear Transfer Nuclear transfer is similar to microinjection; however, instead of injecting the genetic construct into a recipient egg, the genetic construct is initially transferred to a cell line. Once in the cell line, the entire nucleus containing the genetic construct is removed and transferred to an egg with its nucleus removed. The fertilized egg is placed into a foster recipient and a normal pregnancy ensues. Transgenics Transgenics is the area of biology in which recombinant genes are placed into the germ line of living organisms. Nexia uses transgenic biology to transfer specific genes of interest into mice (gene testing) or goats (protein production). As mentioned above, a number of methods, such as nuclear transfer or microinjection, can be used to transfer the genetic material. Once a transgenic fertilized egg is transferred to the foster recipient, a normal pregnancy ensues. Gestation time for goats is approximately 5 months. The kids produced from such a pregnancy may carry the gene of interest and are considered founder animals. If the founder is female, she will produce the protein in her milk when she lactates. Male founders also carry the gene of interest, but are unable to express it. These males are used to produce a second generation of females able to express the gene of interest via sexual reproduction. To encourage the genetic diversity, male founder goats (small BELE® goats) are mated to larger standard female goats, which also serves to increase the milk yield per day.
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