Transgenic and Cloned Organisms By: Michael and Legae
Definition• The term transgenic • Cloned organisms are organism refers to an any organism whose organism in which there genetic information is has been a identical to that of a deliberate/artificial parent organism from modification of the which it was created. genome.
How transgenesis works• Foreign DNA is introduced into the organism and must then be transmitted through the germ line so that every cell, including germ cells, of the organism contain the same modified genetic material.• If the germ cell line is altered, characters will be passed on to succeeding generations in normal reproduction but if the somatic cell line alone is altered, only the organism itself will be affected, not its offspring. – **germ line: genetic material in a cell lineage that is passed down through the gametes before it is modified by somatic recombination or maturation.
There are three ways in which transgenesis can be done. DNA Microinjection ; Retrovirus-mediated Gene TransferEmbryonic Stem Cell-mediated Gene Transfer
DNA microinjection• The DNA or selected gene is introduced by microinjection through a fine glass needle into the male pronucleus - the nucleus provided by the sperm before fusion with the nucleus of the egg.• After fertilization the manipulated fertilized ovum is transferred into the oviduct of a recipient female, or foster mother that has been induced to act as a recipient.
Embryonic stem cell-mediated gene transfer• This method involves prior insertion of the desired DNA sequence by homologous recombination into an in vitro culture of embryonic stem cells.• Stem cells are undifferentiated cells that have the potential to differentiate into any type of cell (somatic and germ cells) and therefore to give rise to a complete organism. These cells are then incorporated into an embryo at the blastocyst stage of development.
Retrovirus-mediated gene transfer• In this method the gene transfer is mediated by means of a carrier or vector, generally a virus or a plasmid. Retroviruses are commonly used as vectors to transfer genetic material into the cell, taking advantage of their ability to infect host cells in this way. Offspring derived from this method are chimeric, i.e., not all cells carry the retrovirus.• Transmission of the transgene is possible only if the retrovirus integrates into some of the germ cells.
For any of these techniques thesuccess rate in terms of live birth of animals containing the transgene is extremely low.
Uses of transgenic organisms• Improving plants New plant varieties have been produced using bacterial or viral genes that confer tolerance to insect or disease pests and allow plants to tolerate herbicides, making the herbicide more selective in its action against weeds and allowing farmers to use less herbicide.• Improving livestock to produce animals that are larger and leaner, grow faster and are more efficient at using feed, more productive, or more resistant to disease.• Pharmaceutical products many valuable pharmaceutical products can now be made using transgenic animals such as mice, rabbits, sheep, goats, pigs and cows. i.e haemoglobin as a blood substitute human protein C, cystic fibrosis transmembrane conductance regulator (CFTR) for treatment of CF, insulin for diabetes treatment, growth hormones for treatment of deficiencies monoclonal antibodies vaccines (antigens).
Cloned Organisms• Def: What exactly is cloning?• Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two.• Methods:Artificial Embryo Twinning Somatic Cell Nuclear Transfer
Artificial Embryo Twinning• relatively low-tech version of cloning. • Artificial embryo twinning uses the As the name suggests, it mimics the same approach, but it occurs in a natural process of creating identical Petri dish instead of in the mothers twins. body. This is accomplished by manually separating a very early• In nature, twins occur just after embryo into individual cells, and then fertilization of an egg cell by a sperm allowing each cell to divide and cell. In rare cases, when the resulting develop on its own. The resulting fertilized egg, called a zygote, tries to embryos are placed into a surrogate divide into a two-celled embryo, the mother, where they are carried to two cells separate. Each cell term and delivered. Again, since all continues dividing on its the embryos came from the same own, ultimately developing into a zygote, they are genetically identical. separate individual within the mother. Since the two cells came from the same zygote, the resulting individuals are genetically identical.
Somatic Cell Nuclear Transfer (SCNT)1] extract the nucleus of a somatic cell, a cell • An embryo is composed of cells thatwhich can come from anywhere in the contain two complete sets ofbody, and insert it into an egg which has hadits nucleus removed. chromosomes. The difference between http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/images/enucleation.mpg ; fertilization and SCNT lies in where those http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning /images/transfer.mpg two sets originated. • In fertilization, the sperm and egg both2] The egg is stimulated ( treated withchemicals or electric current in order to contain one set of chromosomes. Whenstimulate cell division) the sperm and egg join, the resulting http://learn.genetics.utah.edu/content/tech/cloning/whatisclonin zygote ends up with two sets - one from g/scnt.html the father (sperm) and one from the3]it begins dividing and growing, developing mother (egg).into an embryo. • In SCNT, the egg cells single set of chromosomes is removed and replaced by4] It is then implanted into a gestational the nucleus from a somatic cell, whichsurrogate and carried to term. already contains two complete sets of chromosomes. Therefore, in the resultingHow does SCNT differ from the natural embryo, both sets of chromosomes comeway of making an embryo? from the somatic cell.
Question: Are Clones Normal?• Essentially, all somatic cells in a given organism, other than RBCs, have a nucleus with chromosomes that contain exactly the same DNA sequence. But there are hundreds of different kinds of cells in the body, and they are different because each cell type selectively uses different parts of the genome.• The DNA in the nucleus transferred into an oocyte requires reprogramming, for example, from functioning as a skin fibroblast to functioning as a one-cell embryo. Little is known about how this reprogramming occurs, except that it often does not get done correctly. This is not surprising, because the one-cell embryo normally programs sperm and oocyte DNA, not DNA from somatic cells.• Most malprogrammed embryos result in embryonic or fetal death. With current SCNT procedures, this result occurs in nearly 90% of embryos; it is one of nature’s ways of weeding out problems!
• two major problems: few clones survive to term and those that do are grotesquely large. 1. poor survival rate is influenced by the genetic background of the donor cell 2. the gross overgrowth of clones results from the actual procedure of cloning.http://www.sciencedaily.com/releases/2001/05/010511073756.htm• “While clones are genetically identical, physical characteristics such as size, weight and hair type; and behavioural characteristics may not be the same because the DNA has been modified during the cloning process in such a way that it affects the activity of certain genes.”http://www.sciencedaily.com/releases/2003/04/030416085546.htm• Scientists have known for some time that clones’ observable characteristics and traits can vary, and this variation can be passed on to the next generation.• the genomes of cloned plants carry relatively high frequencies of new DNA sequence mutations that were not present in the genome of the donor plant.http://www.sciencedaily.com/releases/2011/08/110804212931.htm
Cloning and its uses• extinct and near-extinct species could • highly prized domesticated animals be reproduced for zoos and/or could be duplicated to improve food reintroduction into the wild; yields in the dairy, beef, pork, and• http://blogs.discovermagazine.com/sciencenotfiction/2009/04/22/ waking-and-cloning-baby-mammoths/#.UMDayIP0CSc poultry industries;• and winning race animals could be • Commonly employed in post-stages cloned for competition. of transgenesis• Eliminates the need for third-party • Therapuetic cloning: production of egg or sperm for: human embryos for use in research. To harvest stem cells that can be – Couples who (i) have a genetic used to study human development disorder and (ii) reject genetic and to treat disease. screening and selective abortion. • Organ cloning- type of cloning that – Gay/lesbian parents does not currently exist but is – Couples one of whom lacks viable theoretically possible. With organ eggs or sperm cloning, human organs could be grown from a small sample of cells for a specific patient.