The process of “knocking down” an unwanted gene is called gene silencing and can be done through RNA interference (RNAi). RNAi is a way to silence the BLG gene by using specially designed RNA molecules that target the BLG gene's mRNA and make it produce only a very small amount of BLG protein. Gene silencing is carried out by first producing RNAs complementary to the mRNAs that code for the BLG proteins that need to be "knocked down". These RNAs are introduced into the cow's cells. They bind to micro RNAs and Argonaute proteins by a silencing complex. The silencing complex binds to the BLG mRNA by RNA base pairing. This occurs because the RNA introduced into the cell has been specifically created to be complementary to the BLG protein mRNA. This ensures that the silencing complex binds only to the mRNA of this protein. When the silencing complex cleaves the mRNA for the BLG protein, the resulting small mRNA fragments cannot be translated into complete proteins. By splitting mRNAs into fragments that cannot be fully translated into proteins, the BLG gene was "knocked down." However, RNAi does not completely destroy BLG gene expression. Say no to plagiarism. Get a tailor-made essay on "Why Violent Video Games Shouldn't Be Banned"? Get an original essay. Some translation can still occur and therefore BLG proteins are still produced. This means that the BLG gene will still produce a very small amount of BLG protein, so cow's milk will contain low levels of BLG protein. Milk produced from these cows with the BLG gene "knocked out" will no longer contain high levels of BLG protein. When cow's milk is drunk, it will not cause the same extent of allergic reactions in susceptible people because the production of the BLG proteins that cause these reactions has been reduced. There are both advantages and disadvantages to producing a transgenic cow that produces milk containing human myelin sheath protein (a therapeutic protein). The advantages are that the protein can be easily extracted from cows' milk and administered to people suffering from certain human diseases. Human myelin sheath protein can be used to treat these people. This means that these people do not have to live with that disease and as a result may live longer than expected. Another benefit of producing this therapeutic protein in transgenic cows is that a large amount of the protein can be produced. The average dairy cow can produce a large amount of therapeutic protein (approximately 5-10 g/L). Transgenesis is also very economical and it is easy to increase or decrease production to meet demand. Genetic manipulation in cows is more specific than conventional breeding as it is possible to focus on a specific trait and is faster than conventional breeding which is slow and unpredictable. The disadvantages are the time it takes to create a transgenic cow. It takes a long time to generate and validate transgenic cows and this could outweigh the benefits that transgenic cow's milk will have on humans. Additionally, the proteins produced in cow's milk cannot be harvested until lactation begins in the cow. Another disadvantage is that the human gene inserted into the cow's genome (transgene) can affect the cow by altering a gene needed for an important function. This is because the transgene is randomly inserted into a chromosome. Enzyme pathways could be affected and new molecules with unknown effects could result..