Reading...
Play button
Play button
Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
29 Cards in this Set
- Front
- Back
|
Understand these terms
|
- Gel electrophoresis is used to separate proteins or fragments of DNA according to size. -PCR can be used to amplify small amounts of DNA. -DNA profiling involves comparison of DNA. - Genetic modification is carried out by gene transfer between species. -Clones are groups of genetically identical organisms derived from a single original parent cell. - Many plant species and some animal species have natural methods of cloning. - Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells. - Methods have been developed for cloning adult animals using differentiated cells. |
|
|
What are some techniques that scientists use to explore an manipulate DNA?
|
- Polymerase Chain Reaction (PCR) (copying DNA in a laboratory ) - DNA Profiling (using DNA to reveal its owner’s identity) - Gene sequencing/Genome Project (mapping DNA by finding where every A, T, C, and G is ) - Gene transfer (cutting and pasting genes to make new organisms) -cloning cells and animals |
|
|
What is gel electrophoresis?
|
This laboratory technique is used to separate fragments of DNA in an effort to identify its origin. Enzymes are used to chop up the long fi laments of DNA into varying sizes of fragments. The DNA fragments are placed into small wells (holes) in the gel, which are aligned along one end. The gel is exposed to an electric current, positive on one side and negative on the other. The effect is that the biggest, heaviest, and least charged particles do not move easily through the gel, so they get stuck very close to the wells they were in at the beginning. The smallest, least massive, and most charged particles pass through the gel to the other side with little diffi culty. Intermediate particles are distributed in between. In the end, the fragments leave a banded pattern of DNA like the one shown in the photo. As seen in Figure 3.35, gel electrophoresis can stop there or a hybridization probe can be added. A probe, in this case for sickle cell disease, is a known sequence of a complementary DNA sequence that binds with a DNA strand in the gel, revealing the presence of the gene we are interested in. |
|
|
A visual for Gel E.
|
|
|
|
Explain PCR
|
- how to make lots of copies of DNA - PCR is a laboratory technique using a machine called a thermocycler that takes a very small quantity of DNA and copies all the nucleic acids in it to make millions of copies of the DNA (see Figure 3.36). PCR is used to solve the problem of how to get enough DNA to be able to analyse it.When collecting DNA from the scene of a crime or from a cheek smear, often only a very limited number of cells are available. By using PCR, forensics experts or research technicians can obtain millions of copies of the DNA in just a few hours. Such quantities are large enough to analyse, notably using gel electrophoresis. |
|
|
Visual for PCR
|
|
|
|
Explain DNA profiling
|
The process of matching an unknown sample of DNA with a known sample to see if they correspond is called DNA profi ling. This is also sometimes referred to as DNA fi ngerprinting because there are some similarities with identifying fi ngerprints, but the techniques are very different. If, after separation by gel electrophoresis, the pattern of bands formed by two samples of DNA fragments are identical, it means that both most have come from the same individual. If the patterns are similar, it means that the two individuals are probably related.
|
|
|
What are some supplications of DNA profiling?
|
DNA profi ling can be used in paternity suits when the identity of someone’s biological father needs to be known for legal reasons. At a crime scene, forensics specialists can collect samples such as blood or semen, which contain DNA. Gel electrophoresis is used to compare the collected DNA with that of suspects. If they match, the suspect has a lot of explaining to do. If there is no match, the suspect is probably not the person the police are looking for. Criminal cases are sometimes reopened many years after a judgement was originally made, in order to consider new DNA profi ling results. In the USA, this has led to the liberation of many individuals who had been sent to jail for crimes they did not commit. DNA profi ling is used in other circumstances too, for example in studies of ecosystems, when scientists use DNA samples taken from birds, whales, and other organisms to clarify relationships. This has helped establish a better understanding of social relationships, migrating patterns, and nesting habits, for example. In addition the study of DNA in the biosphere has given new credibility to the ideas of evolution: DNA evidence can often reinforce previous evidence of common ancestry based on anatomical similarities between species.
|
|
|
How are DNA profiles analyzed?
|
In the photo on page 158, showing gel electrophoresis of nine samples of DNA, the line marked C2 (child number 2) and the one being pointed to, F (father), show similarities in their banding patterns. However, the children marked C1, C3, and C4 do not show many similarities. From this DNA evidence, it should be clear that person F is much more likely to be the father of child number 2 than of any of the other children. Similar techniques are used to analyse the similarities and differences between DNA collected at a crime scene and DNA samples taken from suspects. The techniques have been perfected to a point where it is possible to determine the identity of someone by examining cells found in the traces of saliva left on the back of a postage stamp on a letter.
|
|
|
What is Genetic Modification
|
Gene transfer between species
|
|
|
Explain Gene transfer
|
The technique of taking a gene out of one organism (the donor organism, e.g. a fi sh) and placing it in another organism (the host organism, e.g. a tomato) is a genetic engineering procedure called gene transfer. Just such a transfer was done to make tomatoes more resistant to cold and frost. It is possible to put one species’ genes into another’s genetic makeup because DNA is universal: as you will recall (Section 2.6), all known living organisms use the bases A, T, C, and G to code for proteins. The codons they form always code for the same amino acids, so transferred DNA codes for the same polypeptide chain in the host organism as it did in the donor organism. In the example above, proteins used by fi sh to resist the icy temperatures of arctic waters are now produced by the modifi ed tomatoes to make them more resistant to cold. Another example of gene transfer is found in Bt corn, which has been genetically engineered to produce toxins that kill the bugs that attack it. The gene, as well as the name, comes from a soil bacterium, Bacillus thuringiensis, which has the ability to produce a protein that is fatal to the larvae of certain crop-eating pests.
|
|
|
What is cloning?
|
cutting, copying and pasting genes
|
|
|
Explain cutting and pasting DNA
|
The ‘scissors’ used for cutting base sequences are enzymes. Restriction enzymes called endonucleases fi nd and recognize a specifi c sequence of base pairs along the DNA molecule. Some can locate target sequences that are sets of four base pairs, others locate sets of six pairs. The endonucleases cut the DNA at specifi ed points. If both the beginning and the end of a gene are cut, the gene is released and can be removed from the donor organism. For pasting genes, the enzyme used is called DNA ligase. It recognizes the parts of the base sequences that are supposed to be linked together, called the sticky ends, and attaches them.
|
|
|
Explain Copying DNA (DNA cloning)
|
Copying DNA is more complex, because a host cell is needed in addition to the cutting and pasting enzymes described above. Although yeast cells can be used as host cells, the most popular candidate in genetic engineering is the bacterium Escherichia coli. Like other prokaryotes, most of the genetic information for E. coli is in the bacterium’s single chromosome. However, some DNA is found in structures called plasmids. Plasmids are small circles of extra copies of DNA fl oating around inside the cell’s cytoplasm. To copy a gene, it must be glued into a plasmid. To do this, a plasmid is removed from the host cell and cut open using a restriction endonuclease. The gene to be copied is placed inside the open plasmid. This process is sometimes called gene splicing. The gene is pasted into the plasmid using DNA ligase. The plasmid is now called a recombinant plasmid and it can be used as a vector, a tool for introducing a new gene into an organism’s genetic makeup.In the final step needed for copying (or cloning) the gene, the vector is placed inside the host bacterium and the bacterium is given its ideal conditions in which to grow and proliferate. This is done by putting the bacterium into a bioreactor, a vat of nutritious liquid kept at a warm temperature. Not only does the host cell make copies of the gene as it reproduces, but because the gene is now in its genetic makeup, the modifi ed E. coli cell expresses the gene and synthesizes whatever protein the gene codes for. This process has been used successfully to get E. coli to make human insulin, a protein needed to treat diabetes (see Section 2.7). The older technique for obtaining insulin involves extracting it from cow and pig carcasses from the meat industry, but this has caused allergy problems. Using recombinant human DNA avoids that problem.
|
|
|
A diagram for cloning
|
|
|
|
What is GMO?
|
A genetically modifi ed organism (GMO) is one that has had an artifi cial genetic change made using the techniques of genetic engineering, such as gene transfer or recombinant DNA as described above. One of the main reasons for producing a GMO is so that it can be more competitive in food production. Another common reason is to ‘teach’ a bacterium to produce proteins that are useful in medical applications, as we saw with insulin.
|
|
|
What are transgenic plants?
|
The simplest kind of genetically modifi ed (GM) food is one in which an undesirable gene has been removed. In some cases, another, more desirable, gene is put in its place, while in other cases only the introduction of a new gene is needed, no DNA has to be removed. Whichever technique is applied, the end result is either that the organism no longer shows the undesired trait or that it shows a trait that genetic engineers want. The fi rst commercial example of a GM food was the Flavr Savr tomato. It was fi rst sold in the USA in 1994, and had been genetically modifi ed to delay the ripening and rotting process so that it would stay fresher longer. Although it was an ingenious idea, the company lost so much money from the project that it was abandoned a few years later. Another species of tomato was modifi ed by a bioengineering company to make it more tolerant to higher levels of salt in the soil. This made it easier to grow in areas with high salinity. One of the claims of the biotech industry is that GM foods will help solve the problem of world hunger, by allowing farmers to grow foods in various, otherwise unsuitable, environments. Critics point out that the problem of hunger in the world is one of food distribution, not food production. Another plant of potential interest to the developing world is a genetically modifi ed rice plant that has been engineered to produce beta carotene in the rice grains. The aim is that the people who eat this rice will not be defi cient in vitamin A (the body uses beta carotene to form vitamin A).
|
|
|
What are transgenic animals?
|
One way of genetically engineering an animal is to get it to produce a substance that can be used in medical treatments. Consider the problem faced by people with haemophilia. The reason their blood does not clot is because they lack a protein called factor IX. If such people could be supplied with factor IX, their problem would be solved. The least expensive way of producing large amounts of factor IX is to use transgenic sheep. If a gene that codes for the production of factor IX is associated with the genetic information for milk production in a female sheep, she will produce that protein in her milk. In the future, a wide variety of genetic modifi cations may be possible, perhaps inserting genes to make animals more resistant to parasites, to make sheep produce pre-dyed wool of any chosen colour, to produce prize-winning show dogs, faster racehorses … The possibilities seem almost boundless, and it is diffi cult to imagine what the future might be like.
|
|
|
What are some natural methods of cloning?
|
Nature invented cloning long before humans did. Certain plants, such as strawberry plants, can send out horizontal structures to allow a new strawberry plant to grow a short distance from the original plant. The new plant will be an exact genetic copy of the first one, because only one parent was involved and no meiosis and fertilization was used to add variety to the genetic makeup of the plant.If planted in the ground, a potato will grow into a new plant. The plant will be genetically identical to (will be a clone of) the original potato plant. This is an advantage for the plant, because there is no need to rely on pollen to fertilize the fl owers, but it can be a disadvantage, because if all potato plants in a population are clones, it means that not only do they have the same good qualities, they also have the same weaknesses. If the population is attacked by a pathogen such as potato blight, it could wipe out the population. Historians will tell you of the dangers of this, notably in Ireland in the middle of the 19th century, when 1 million people died of starvation. Of course, historians will also tell you that there were other causes; history is complex, but the potato blight was a major factor in the famine. What about animals: can they clone themselves the way plants sometimes do? Although this is extremely rare, and exceptional, among certain invertebrates, one animal that is capable of reproducing asexually by making clones of itself is the hydra, Hydra vulgaris. This freshwater organism is in the same phylum as sea jellies, sea anemones, and coral polyps. If food sources are plentiful, small buds will form on its body, develop into adults, and break off to form new, genetically identical, hydra. This process is called budding, and you may have observed this in electron micrographs of yeast cells. Similar to the plant examples (strawberries and potatoes), hydra
|
|
|
Explain how animals can be cloned from embryos?
|
The defi nition of a clone is a group of genetically identical organisms, or a group of cells artifi cially derived from a single parent. In either case, the resulting cells or organisms were made using laboratory techniques. In farming, clones have been made for decades by regenerating plant material or by allowing an in vitro fertilized egg to divide to make copies of itself. When cloning happens naturally in animals (including humans), identical twins are produced. The fi rst evidence of an experimental attempt to make artifi cial clones was performed by Hans Dreisch in the 1890s with sea urchin embryos. He was able to separate cells from a single sea urchin embryo and grow two identical embryos. The aim of his experiment was not to create clones but, looking back, we can say that he serendipitously invented a new technique. Serendipity is a good concept to understand in science. It refers to an unexpected but positive discovery and happens when someone is looking for the answer to one question and accidentally fi nds the answer to a completely different question. With the correct laboratory equipment, it is possible to separate cells from a growing embryo of an animal, and place the separated cells in the uterus of a female of that species and get artifi cial twins, triplets, quadruplets, etc., depending on how many cells were separated. Remember that embryonic cells are undifferentiated cells so there is nothing exceptionally astounding about this kind of cloning. Remember, nature has been doing this for a long time by forming identical twins.
|
|
|
Explain how animals can be cloned from adult cells?
|
Until recently, cloning was only possible using genetic information from a fertilized egg cell. After dividing many times, some of the cells will specialize into muscle cells, others into nerves, others into skin, and so on, until a foetus forms. For a long time, it was thought that once a cell has gone through differentiation, it cannot be used to make a clone. But then there was Dolly.
|
|
|
Explain Cloning using a differentiated cells
|
In 1996, a sheep by the name of Dolly was born. She was the first clone whose genetic material did not originate from an egg cell. Here is how researchers at the Roslin Institute in Scotland produced Dolly (see Figure 3.38). 1 From the original donor sheep to be cloned, a somatic cell (non-gamete cell) from the udder was collected and cultured. The nucleus was removed from a cultured cell. 2 An unfertilized egg was collected from another sheep and its nucleus was removed. 3 Using an electrical current, the egg cell and the nucleus from the cultured somatic cell were fused together. 4 The new cell developed in vitro in a similar way to a zygote, and started to form an embryo. 5 The embryo was placed in the womb of a surrogate mother sheep. 6 The embryo developed normally. 7 Dolly was born, and was presented to the world as a clone of the original donor sheep. This kind of cloning is called reproductive cloning because it makes an entire individual. The specifi c technique of reproductive cloning is called somatic cell nuclear transfer, because it uses a cell that is not an egg cell (therefore it is a somatic cell), and it has had its nucleus removed and replaced by another nucleus. |
|
|
A visual of Dolly and cloning
|
|
|
|
Explain cloning using undifferentiated cells
|
In some cases, scientists are not interested in making an organism but simply in making copies of cells. This second type of cloning is called therapeutic cloning, and its aim is to develop cells that have not yet gone through the process of differentiation. As the fi rst technique in this area involved using embryos, the cells are referred to as embryonic stem cells, and the branch of laboratory work that investigates therapeutic cloning is called stem cell research.
|
|
|
What are some ethical issues surrounding therapeutic cloning?
|
Because therapeutic cloning starts with the production of human embryos, it raises fundamental issues of right and wrong. Is it ethically acceptable to generate a new human embryo for the sole purpose of medical research? In nature, embryos are created only for reproduction, and many people believe that using them for experiments is unnatural and wrong. However, the use of embryonic stem cells has led to major breakthroughs in the understanding of human biology. What was once pure fi ction is coming closer and closer to becoming an everyday reality, thanks to stem cell research. Some of the aims of current research are to be able to grow: • skin to repair a serious burn • new heart muscle to repair an ailing heart • new kidney tissue to rebuild a failing kidney. With very rare exceptions, the vast majority of researchers and medical professionals are against the idea of reproductive cloning in humans. However, there is a growing popularity for therapeutic cloning because the potential of stem cell research is so enticing.
|
|
|
Explain why PCR Is necessary?
|
Analysis of DNA samples using techniques such as gel electrophoresis cannot be done with only a few strands of DNA. When DNA samples are collected, for example at a crime scene, sometimes only a few cells are found. To obtain enough copies for analysis, the DNA strands must be copied millions of times
|
|
|
Explain the central ethical issue concerning stem cell research.
|
Typically, the source of stem cells is human embryos. The ethical question is: ‘Can we use embryos purely as research tools?’ Critics argue that these balls of cells should be treated with respect and dignity because they are of human origin and their natural destiny is to try to develop into baby girls or boys, so using them for another purpose is unnatural and unethical
|
|
|
Justify whether the benefits outweigh the risks in genetically modifying plants and animals.
|
Answers will vary, but both benefits (e.g. a plant’s resistance to drought, higher yield) and risks (e.g. consequences of GM pollen escaping, possible allergies) should be explored, and there should be a justification in the answer.
|
|
|
Look at the foods in your house. Are food labels today effective at indicating whether or not the food is genetically modified? Justify your answer
|
Answers will vary, but it is generally agreed that the labelling in most countries is insufficient for consumers to make educated choices about the foods they buy. For example, labels could say ‘may contain GM soybeans’ but it is not clear what percentage could be expected
|
