Biology: Chapter 11 Review Genetic Engineering Gene Technology

The process of manipulating genes for practical purposes is called genetic engineering. Genetic engineering may involve building recombinant DNA; DNA made from two or more different organisms. ____________________________ Today, the human insulin gene is transferred to bacteria through genetic engineering. Because the code is universal, bacteria can transcribe and translate a human insulin gene using the same code a human cell uses in order to produce human insulin.

Restrictive enzymes are bacterial enzymes that recognize and bind to specific short sequences of DNA, and than cut the DNA between specific nucleotides. The DNA from a vector is also cut. A vector is an agent that is used to carry the gene of interest into another cell. Plasmids are circular DNA molecules that can replicate independently of the main chromosomes of the bacteria. The DNA fragments from the organism containing the gene of interest are combined with the DNA fragments from the vectors.

In our example, the DNA fragments are combined with plasmid DNA fragments. We develop a hybrid plasmid made of both parts. The host cells than take up the recombinant DNA, this plasmid hybrid. ______________________________ In a process called gene cloning, many copies of the gene of interest are made each time the host cell reproduces. By fission. Cells that have received the particular gene of interest are separated from cells that did not take up the vector with the gene of interest.

The Human Genome Project is a research project linking 20 labs in six countries. Teams of scientists in the project worked to identify and map all 3.2 billion base pairs of all the DNA that makes up the human genome. _______________________________ Exons are scattered about the human genome in clumps that are not spread out evenly among the chromosomes. On most human chromosomes, great stretches of untranscribed DNA fill the chromosomes between the scattered clusters of transcribed genes. These untranscribed areas are like blank recording tape.

Human cells contain about 30,000 to 40,000 genes Human cells contain about 30,000 to 40,000 genes. This is only about double the number of genes in a fruit fly. It is only about one quarter of the 120,000 genes scientists had expected to find. _________________________________ Drugs: Many genetic disorders and human illnesses occur when the body fails to make critical proteins. Today, many genetically engineered medicines are used to treat everything from burns to diabetes. Examples include: Erythropoetin for anemia, Growth factors for treating burns, ulcers, Human Growth Hormone for growth defects, Insulin for diabetes, Interferons for viral infections and cancer, Taxol for ovarian cancer

Many viral diseases, such as smallpox and polio, cannot be treated by existing drugs. Instead, they are combated by prevention through use of vaccines. A vaccine is a solution containing all or part of a harmless version of a pathogen (disease-causing microorganism). It is a weakened version of the disease; incapable of causing serious harm. When a vaccine is injected, the immune system reads the pathogen and responds by making defensive proteins called antibodies. The immune system creates a defense system against this form of the disease. In the future, if the same pathogen enters the body, the antibodies are now there to combat the pathogen and stop it’s growth before it can cause a disease. The immune system stays in place so when the flu or cold strikes in full force, the antibodies are already there to fight it before it can grow. .

With these types of vaccines there is always some small danger for getting sick as some people are more sensitive to the vaccine. Their threshold is low. Vaccines made by genetic engineering avoid this danger and are less likely to risk infection to those who are extra-sensitive to the microbes. ___________________________________________________________ . Dna Fingerprinting: Other than identical twins, no two individuals have the same genetic material. Scientists use DNA sequencing technology to determine a DNA fragment’s nucleotide sequence. Because the places a restrictive enzyme can cut depend on the DNA sequence, the lengths of the DNA fragments will vary between any two individuals. A DNA fingerprint is a pattern of dark bands on photographic film that is made when an individuals DNA restriction fragments are exposed to an X-ray film.

Today, we use genetic engineering to select and add characteristics and modify plants by manipulating a plant’s genes. Genetic engineering can change plants in many ways; from making plants drought resistant to making plants that can thrive in different soils, climates or environmental conditions. Genetic engineers have developed crop plants that are resistant to a biodegradable weedkiller called glyphosate. This enables farmers to spray their fields with glyphosate, kill all the weeds off, and leaves the crops unharmed. Scientists have also developed crops that are resistant to certain insects by inserting specific genes into plants. Genetic engineering has been able, in many instances, to improve the nutritional value of many crops.

Are GM crops harmful to the environment? Risks: Many people, including many scientists, have expressed concern that genetically modified crops (GM crops) might turn out to be dangerous. Potential problems: We have already noted that crops such as soybeans have been genetically altered to make them resistant to the weedkiller glyphosate. Scientists are concerned that the use of glyphosate will lead to weeds that are immune to this weedkiller. _______________________________________________ Are GM crops harmful to the environment? Will genes introduced into crops by genetic engineering pass on to wild varieties of plants? This type of gene flow happens all the time between related plants. In most crops however, no closely related wild version of the plant is nearby to take up the gene changes.

Some scientists fear that insect pests may become immune (by adapting) to the toxins that are genetically engineered in some plants. This would lead to insect strains that are harder to kill as they would be immune to the genetically produced changes that were supposed to repel them. Farmers have, for generations, improved their stock of animals through selection of the best and cross breeding. Now, many farmers use genetically-engineered techniques to improve their stock or their production. Many farmers add growth hormone to the diet of their cows to increase the amount of milk their cows produce. The cow growth hormone gene is introduced into bacteria which is than added to the cow’s food supply. This increases the amount of milk the cow produces.

Another way in which gene technology is used in animal farming is in the addition of human genes to the genes of farm animals to produce human proteins in milk. This is used for complex human proteins that cannot be made by bacteria through gene technology. The human proteins are extracted from the animal’s milk and sold for pharmaceutical purposes. These animals are called transgenic animals because they have human DNA in their cells. _____________________________________________________ More recently, scientists have turned to cloning animals as a way of creating identical animals that can make medically useful proteins. In cloning, the intact nucleus of an embryonic or fetal cell is placed into a new egg whose nucleus has been removed. The egg with the new nucleus is than placed into the uterus of a surrogate mother and is allowed to develop.

In 1997, the first successful cloning using differentiated cells from an adult animal resulted in a cloned sheep named Dolly. A differentiated cell is a cell that has become specialized to become a specific type of cell. In Dolly’s case; a lamb was cloned from the nucleus of a mammary cell taken from an adult sheep. Scientists thought that a differentiated cell would NOT give rise to an entire animal. The cloning of Dolly successfully proved otherwise. An electric shock was used to fuse mammary cells from one sheep with egg cells without nuclei from another sheep. The fused cells divided to form embryos, which were implanted into surrogate mothers. Only one embryo survived the cloning process.

Since Dolly’s birth in 1996, scientists have successfully cloned several animals. Only a few of these cloned animals survive however. Many become fatally oversized. Technical problems with reproductive cloning lie within a developmental process that conditions egg and sperm so that the “right combination of genes” are turned “on” or “off” during early stages of development The process of conditioning the DNA during an early stage of development is called genomic imprinting. In genomic imprinting, chemical changes made to DNA prevent a gene’s expression without altering it’s sequence.

Usually, a gene is locked into the “off” position by adding methyl groups to it’s cytosine nucleotides. The bulky methyl groups prevent polymerase enzymes from reading the gene, so the gene cannot be transcribed. Later in development, the methyl groups are removed and the gene is reactivated. Normal vertebrae development depends on precise genomic imprinting. This process, which takes place in adult reproductive tissue, takes months for sperm and years for eggs. Reproductive cloning fails because the reconstituted egg begins to divide within minutes. There is simply not enough time in these few minutes for the reprogramming to process properly. Because of these technical problems; and because of ethical problems, efforts to clone humans are illegal in most countries.