9.3 Blueprint of life: 5. Current reproductive technologies
|Syllabus reference (October 2002 version)|
5. Current reproductive technologies and genetic engineering have the potential to alter the path of evolution
Students learn to:
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 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.
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.
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, GH (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
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, GH ( growth hormone), is incorporated into the genes of salmon.
A pea gene for lectin has been incorporated into potato plants.
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