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9.3 Blueprint of life: 5. Current reproductive technologies
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5. Current reproductive technologies and genetic
engineering have the potential to alter the path of
evolution
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Students learn to:
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Students: |
Extract from Biology Stage 6 Syllabus (Amended October
2002). © Board of Studies, NSW.
[Edit: 10 Jun 10]
Background Information
Reproductive technologies include artificial insemination, artificial pollination and cloning. Genetic engineering aims to move genetic material (usually single genes) from one organism and introduce it into the genetic complement of another, thus producing a transgenic organism. The technologies together have meant that the process of natural selection no longer dictates the direction of evolution. Indeed, genes are now moving across species barriers. This brings the possibility of improved crop and livestock yields to feed starving populations, as well as a possible end to the suffering of people with incurable genetic diseases. This technology also has its critics who feel that the new transgenic species could bring with them unforeseen ecological and medical disasters.
identify how the following current reproductive techniques may alter the genetic composition of a population:
- artificial insemination
- artificial pollination
- cloning
- In the case of all the technologies mentioned, the donor gametes or body cells have been carefully selected for predetermined characteristics – or artificially selected. In most cases, one exemplary donor contributes all the genetic material and this results in uniform offspring. Over generations, genetic variability within the species has been reduced.
process information from secondary sources to describe a methodology used in cloning organisms
Background
Cloning is the process of making genetically identical copies of an organism without using the process of sexual reproduction. Both plants and animals have been successfully cloned.
- To process information you will need to gather information on cloning methodologies. The very latest information will be available in scientific journals and on the Internet. However, this has been quite topical lately so there should be information in some of the popular journals. When you have enough information, you will need to compare the different sources and decide if some are more reliable than others.
Methodology used in cloning organisms
Recently, plants have been cloned using tissue culture propagation. Tissue from the roots is taken and the root cells separated. These cells are then grown (cultured) in a nutrient-rich medium where they become unspecialised. The unspecialised cells are called calluses. After treatment with the appropriate plant hormones, the calluses are able to develop into seedlings, that go on to grow into fully mature plants. These plants are genetically identical to the original ‘parent’ plant. Rare orchids have been cultured and grown in this manner. A more recent example, has been the cloning of tissue from the Wollemi Pine. This rare pine, thought to be extinct but now has been discovered in the Blue Mountains region of NSWand successfully cloned. These cloned offspring are being cultivated in the Royal Botanic Gardens in Sydney and sold to the public for planting in gardens. Thus, the species, which has few numbers in the wild, can be preserved.
In animals, progress in cloning species has not been as rapid. Current techniques require an unfertilised egg to act as a ‘host’ for genetic material from a specialised cell. The donor egg has had its nucleus physically removed, and the nucleus from a cell of the species to be cloned is inserted. An electrical stimulus is used to fuse the nucleus with the egg cell and to stimulate cell division. At a certain stage in cell division, the embryo is introduced into a surrogate mother where it continues its development. When born the clone is genetically identical to the animal that donated the original nucleus. Cloning of animals was first performed with tadpoles by John Gurdon in the 1970’s. The tadpoles did not survive to grow into adult frogs. Dolly the sheep was the first successfully cloned mammal in 1997. Since then, other species have been cloned.
outline the processes used to produce
transgenic species and include examples of this process and
reasons for its use
Transgenic organisms contain a gene (transgene) from another species. This is acheived through recombinant DNA technology. Recombinant DNA technology manipulates DNA by the use of restriction enzymes, ligases and PCR (polymerase chain reaction). Restriction enzymes are used to cut DNA in specific places. These enzymes are also known as gene scissors or gene shears. Different restriction enzymes cut DNA in specific parts. The cut ends are known as 'sticky ends'. Ligases are used to repair and strengthen DNA especially after it has been cut by restriction enzymes. PCR is used to produce many copies of the recombinant DNA formed by the previous processes.
Once the recombinant DNA is produced there are processes used to insert the DNA into the host species. These processes include microinjection, Ti plasmid insertion, gene gun and electroporation.
In microinjection a fine glass needle is used to insert the recombinant DNA into the nucleus of the host cell.
Ti (tumour inducing) plasmid insertion uses a bacterium called Agrobacterium tumefaciens. These bacteria produce crown gall in plants by inserting some of their own DNA into the host DNA causing the plant to produce a gall in which the bacteria live. The ability of the bacteria to insert DNA is used to transfer DNA into the host species.
The gene gun blasts small metal pieces coated with DNA into the nucleus of the host cell.
Electroporation uses electric pulses to create small pores in the nuclear membrane through which DNA is inserted.
Examples of transgenic species are genetically engineered salmon which have the gene coding for the protein, bGH (bovine growth hormone), and potato plants which have a pea gene for lectin inserted.
analyse information from secondary sources to identify examples of the use of transgenic species and use available evidence< to debate the ethical issues arising from the development and use of transgenic species
- Analyse information that describes examples of the use of transgenic species to find evidence that should be part of a balanced debate on the ethical issues arising from the development and use of transgenic species. Some starting web sites are provided below.
- Be critical in identifying and evaluating the quality of scientific evidence provided. Carefully check printed material for scientific rigor. There are few checks on material published on the web. Look for information about the credentials of the authors of the information you are reviewing.
Ethical Issues in Genetic Engineering and Transgenics
by
Linda MacDonald Glenn,
An ActionBioscience.org original article, USA, June 2004
Bumpy Road for Biotech
Rachel's Environment and Health News #760
January 30, 2003, USA
How Safe is GM Food? Editorial, The Lancet, Vol 360,
Number 9342, October 26, 2002, UK S
Some ethical issues arising from the development and use of transgenic species
Transgenic organisms are those that have DNA derived from another species incorporated into their genetic complement. This is done by genetic engineering techniques. Both plants and animals have been genetically modified to create ‘improved’ strains of a particular species.
The following are two examples.
Genetically engineered salmon:
The gene coding for the protein, bGH (bovine growth hormone), is incorporated into the genes of salmon.
- Outcome – larger, faster growing fish
- Evaluation – Possible farmed source of fish as food. However, the fish are kept in ponds that offer no escape to the wild because there is much concern that they will upset or destroy natural ecosystems.
Potato plants:
A pea gene for lectin has been incorporated into potato plants.
- Outcome – protection against insect attack. Lectin is a protein which interferes with digestion in insects. It is termed an ‘antifeedant’.
- Evaluation – As potatoes are a staple food source for many populations throughout the world, it is important to maintain and increase production. Protection against insect attack improves the success of growing potatoes. Concerns exist about controlling the ‘escape’ of these transgenic potatoes into the wild as the technology is only recent and long-term impacts on the environment have yet to be observed or evaluated.
discuss the potential impact of the use of reproduction technologies on genetic diversity of species using a named plant and animal example that have been genetically altered
- Reproductive technologies, such as cloning, and the engineering of transgenic species have the potential to both increase and decrease genetic diversity. By moving genes from species to species, the genetic diversity is being increased. Crops, such as rice, have been genetically engineered to suit a particular climate and topography, making then resistant to herbicides and pesticides commonly used in a particular region.
- Transgenic animals present greater problems with lower success rates so far. One important use is seen to be the preservation of numbers of endangered species. The first cloned endangered mammal was a guar (an endangered wild ox from SE Asia), but unfortunately it did not survive. It is hoped that reproductive technologies such as cloning and sperm and embryo banks can be used to preserve stocks of threatened species.
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