4.4c Cloning & GMOs
27/02/2013 § Leave a comment
Cloning, just like most everything else in the world, has its upsides and downsides. The point of cloning is to produce an identical copy of genes, cells or organisms and is especially beneficial if the set that is copied has desirable combinations of characteristics. Products of cloning are obviously called clones, specifically defined as a grope of genetically identical organisms or a group of genetically identical cells derived from a single parent cell. Plants are more easily cloned than animals – they’re cloned through pieces of root, stem or leaf. In livestock, eggs can be fertilized to develop into a multicellular embryo. The cells in the embryo can then be separated while they were all pluripotent, aka capable of developing into any type of tissue. The first successful mammal cloning from adult cells was Dolly the sheep.
Scientists are currently trying to develop ways to make cloning useful in a medical sense. There is already therapeutic cloning in humans that can replace tissues or even organs that have been lost or damaged. There are huge controversies and ethical issues with these processes, though. On one side, the benefits of therapeutic cloning are:
- the embryonic stem cells can be used to save lives and reduce suffering
- cells can be removed from non-developing embryos that would have died anyway
- cells are removed when the embryo doesn’t feel anything
On the other side, the arguments against therapeutic cloning are:
- every embryo has the chance to be a human being and so should be allowed to develop into one
- more embryos produced than needed; some need to be disposed of (killed)
- always the danger of stem cells losing control and developing into a tumor
Finally, the Human Genome Project (HGP) is an international project that aims to locate all of the genes on the human chromosome. It was assumed that there were about 100,000 genes on the human genome but there are really only between 25,000 to 30,000. Should the scientists succeed in mapping the entire human genome, they’d be able to identify genetic diseases, which means they could produce drugs based on the DNA sequences. This project could potentially open a whole new set of doors for evolutionary scientists and geneticists. I mean, I think it’s pretty cool.
- Calculate and predict; genotypic and phenotypic ratios of offspring of dihybrid crosses involving unlinked autosomal genes.
- Identify which of the offspring in dihybrid crosses are recombinants.
- Describe the methods and aims of DNA profiling.
- Outline a technique for transferring genes between species.
- Describe the technique for the transfer of the insulin gene using E. coli.
- Discuss the potential benefits and possible harmful effects of genetic modification.
- Discuss the ethical arguments for and against the cloning of humans.
- Outline the ethical issues of cloning humans.
DATA BASED QUESTIONS
Page 171, comparing mouse and human genomes
[Figure 12] shows all of the types of chromosome in mice and humans. Numbers and colours are used to indicate sections of mouse chromosomes that are homologous to sections of human chromosomes.
1. Deduce the diploid chromosome number of mice. —> 42
2. Identify the two human chromosome types that are most similar to mouse chromosomes. —> The X and Y chromosomes are the most similar between human and mouse chromosomes.
3. Identify mouse chromosomes which contain sections that are not homologous to human chromosomes. —> Mouse chromosome 7 is far from human chromosome 7. Mouse chromosome 13 is very different from human chromosome 13. Human chromosomes 15 to 17 are also very different from those of the mouse’s genome.
4. Suggest reasons for the many similarities between mouse and human genomes. —> Mice and humans need to do different tasks/functions in life. Mice need to scamper around quickly on four feet to find food but humans need to toil, labour and work. Humans are larger than mice and would need a few more genes to code for those characteristics. Mice are also on a very different diet from humans and would therefore need different proteins from us – genes code for that, too.
5. Deduce how chromosomes have mutated during the evolution of animals such as mice and humans. —> Chromosomes could have mutated naturally through substitution. They could also have been affected by the environment around the mice’s and humans’ predecessors.
Page 172, determining an open reading frame
Once the sequences of bases in a piece of DNA has been determined, a researcher may want to locate a gene. To do this, computers search through the sequences looking for open reading frames. An open reading frame is one that is uninterrupted by stop sequences and could therefore code for the production of a protein. The stop codons are UGA, UAA, and UAG.
1. State the number of codons in the genetic code. —> 11 codons
2. Determine the fraction of codons that are stop codons in the genetic code. —> 2/11 codons are stop codons in this genetic code
3. [In Table 2,] the codons could start with the first, second, or third base. These correspond to three different reading frames (RF1, RF2, RF3). Determine which of the reading frames, 1, 2, or 3 above, might be an open reading frame. —> None of the frames are open reading frames because of the UGA sequence within the first ten bases.
Chapter 14 Questions
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1. The cheetah (Acinonyx jubatus) is an endangered species of large cat found in South and East Africa. A study of the level of variation of the cheetah gene pool was carried out. In one part of this study, blood samples were taken from 19 cheetahs and analyzed for the protein transferrin using gel electrophoresis. The results were compared with the electrophoresis patterns for blood samples from 19 domestic cats (Felix sylvestris). Gel electrophoresis can be used to separate proteins using the same principles as in DNA profiling. The bands on the gel which represent forms of the protein transferrin are indicated.
NOW DEDUCE THIS:
- a) the number of domestic cats and the number of cheetahs that were heterozygous for the transferrin gene; —> 13 domestic cats, 0 cheetahs
- b) the number of alleles of the transferrin gene in the gene pool of domestic cats; —> 3 – 4 alleles
- c) the number of alleles of the transferrin gene in the gene pool of cheetahs —> 1
2. Outline two uses of restriction enzymes in biotechnology. —> Restriction enzymes are used to produce GMOs (genetically modified organisms). The same enzyme cuts both the host DNA and the donor DNA, which are then combined together with DNA ligase. Restriction enzymes are used in DNA profiling; where the sample DNA is cut with a restriction enzyme for amplification. Different individuals will show different patterns in their fragments. These fragments are separated by gel electrophoresis.
3. Suggest why therapeutic cloning might be opposed by advocates of women’s rights. —> Eggs are necessary, and harvesting eggs is a exploitation of privacy; women would have to offer up their eggs for therapeutic cloning; might result in pregnancies.
4. Compare the polymerase chain reaction with DNA replication as it occurs in cells. —> In both processes, the polymerase enzyme is used to add nucleotides to the growing chain. Both processes are semi-conservative. A primer is needed in both processes. Replication works with the entire genome. PCR amplifies only a fragment of the DNA. In the PCR, the DNA is denatured with heat (!) but in replication, the helicase is used to denature/unwind DNA.
5. List three examples of where cloning occurs naturally. —> during mitosis, when the chromosomes are replicated; during prophase I in meiosis, when the chromosomes are replicated; during growth, our cells clone each other; asexual reproduction; binary fission amongst bacteria; monozygotic twins (whut)
6. [Figure 17] shows the results of DNA profiling of a family consisting of a man, a woman, and their four children.
- a) Explain which fragment is the smallest. —> fragment IV
- b) Deduce which child is not the biological offspring of the father. —> child 2
7. What are functions of the polymerase chain reaction? —> A
- i) To copy fragments of DNA.
- ii) To amplify fragments of DNA.
- iii) To translate fragments of DNA.
A (i and ii only), B (i and iii only), C (ii and iii only), D (i, ii, and iii)