Highlights Transgenics and Cloning II
1. Making transgenic organisms involves a number of technical challenges. Ideally, a transgenic organism as the altered DNA in every one of their cells. Doing this in a mature organism is difficult because getting the desired DNA into every cell is not easy. One strategy for doing this is to use an altered retrovirus to infect cells and insert DNA into the host chromosome. To do this, the original retrovirus carrying the DNA must be altered so as not to cause other problems.
2. Another mechanism for getting DNA into all cells of an organism is to use nuclear microinjection (called pronuclear microinjection by your book). In this method, a syringe with a nanoscopic "needle" is inserted into a cell and material is added to the cytoplasm. In some cases, such as the cloning of an organism, contents of a cell might be removed, such as the nucleus.
3. Getting eukaryotic cells to make desired proteins is important. Not all proteins useful to humans can be produced by bacteria, due to the fact that many human (and other eukaryotic proteins) are chemically modified and bacteria do not normally do this. To make a eukaryotic organism make a desired protein requires making a transgenic animal that contains the desired gene to be made. Examples of genes made by eukaryotic organisms include t-PA in milk (mice or cows are often used), blood clotting factors in goat milk, and human insulin in chicken eggs. In each case, a recombinant mouse, cow, goat, or chicken had to be made to carry the desired human gene. (Note - t-PA is an important factor for breaking blood clots. Clotting factor is important for hemophiliacs. Insulin is important for diabetics).
4. Transgenic organisms with unusual factors can be made. Examples include the Glo-fish, which was the first transgenic organism available for general sale.
5. Biosensors are systems that use living cells to measure things in the environment. The color a cell changes or the appearance change that a cell undergoes in response to a compound in the environment is a powerful and sensitive measure of that compound. In many cases, the biosensor may be more sensitive and/or broader in ability to recognize environmental pollutants. Fish scales are one system people use to measure for toxic compounds in water. Biosensors are very useful for protecting against bioterrorism because they can indicate the presence of many compounds, not just one.
6. The term "knockout mice" refers to useful laboratory organisms that we can make that lake a specific gene. As noted previously, being able to remove a gene allows researchers to see in an organism what the function of that gene is.
7. To make a knockout mouse, one alters the DNA in a fertilized egg of a mouse. That fertilized egg is allowed to divide a few times and then the cells are mixed with the cells of a normal embryo. A hybrid animal results containing some cells lacking the specific gene and the other cells containing it. If the hybrid animal has cells lacking the gene making up gametes, those gametes can be used to fertilize the gametes of another animal of the opposite sex also lacking those gametes. The resulting fertilized embryo will completely lack the specific gene.
7. Cloning of organisms is increasingly occurring. Among higher animals, Dolly the sheep was the first higher organism to be cloned.
8. Cloning of humans is neither ethical, nor legal.
9. Cloning of organisms is very inefficient. Only a tiny percentage of the attempted clones results in a cloned organism.
10. Cloning offers the benefits of creating an organism with all of the desired traits of the parent.
11. To clone an organism, one takes an egg cell and removes the nucleus. In its place, a nucleus from a cell of the organism to be cloned is inserted in its place. The egg cell is allowed to grow and divide and ultimately become a new organism, having the exact genomic DNA of the one whose nucleus was inserted.
12. Even when an organism is cloned, there may be differences from the original parent arising from differences in the DNA of the mitochondria of the egg cell compared to the DNA of the original organism. This is why even identical twins may have slight differences in appearance.
13. Mitochondria are useful for following the female lineage of an organism, due to the fact that sperm do not contain mitochondria. Only egg cells contain mitochondria. On the other hand, the Y chromosome is useful for following male lineages, since females do not have a Y chromosome.