Transgenic and Cloned Organisms

By: Michael and Legae

Definition

• The term transgenic organism refers to an organism in which there has been a deliberate/artificial modification of the genome.

• Cloned organisms are any organism whose genetic information is identical to that of a parent organism from which it was created.

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 Transfer

Embryonic 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 the success 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).

Examples of transgenic organisms

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. As

the name suggests, it mimics the natural process of creating identical twins.

• In nature, twins occur just after fertilization of an egg cell by a sperm cell. In rare cases, when the resulting fertilized egg, called a zygote, tries to divide into a two-celled embryo, the two cells separate. Each cell continues dividing on its own, ultimately developing into a separate individual within the mother. Since the two cells came from the same zygote, the resulting individuals are genetically identical.

• Artificial embryo twinning uses the same approach, but it occurs in a Petri dish instead of in the mother's body. This is accomplished by manually separating a very early embryo into individual cells, and then allowing each cell to divide and develop on its own. The resulting embryos are placed into a surrogate mother, where they are carried to term and delivered. Again, since all the embryos came from the same zygote, they are genetically identical.

Somatic Cell Nuclear Transfer (SCNT)

1] extract the nucleus of a somatic cell, a cell which can come from anywhere in the body, and insert it into an egg which has had its nucleus removed.

http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/images/enucleation.mpg ; http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/images/transfer.mpg

2] The egg is stimulated ( treated with chemicals or electric current in order to stimulate cell division)

http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/scnt.html

3] it begins dividing and growing, developing into an embryo.

4] It is then implanted into a gestational surrogate and carried to term.

How does SCNT differ from the natural way of making an embryo?

• An embryo is composed of cells that contain two complete sets of chromosomes. The difference between fertilization and SCNT lies in where those two sets originated.

• In fertilization, the sperm and egg both contain one set of chromosomes. When the sperm and egg join, the resulting zygote ends up with two sets - one from the father (sperm) and one from the mother (egg).

• In SCNT, the egg cell's single set of chromosomes is removed and replaced by the nucleus from a somatic cell, which already contains two complete sets of chromosomes. Therefore, in the resulting embryo, both sets of chromosomes come from the somatic cell.

Therapeutic Cloning

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 cell2. 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

be reproduced for zoos and/or reintroduction into the wild;

• http://blogs.discovermagazine.com/sciencenotfiction/2009/04/22/waking-and-cloning-baby-mammoths/#.UMDayIP0CSc

• and winning race animals could be cloned for competition.

• Eliminates the need for third-party egg or sperm for:– Couples who (i) have a genetic

disorder and (ii) reject genetic screening and selective abortion.

– Gay/lesbian parents– Couples one of whom lacks viable

eggs or sperm

• highly prized domesticated animals could be duplicated to improve food yields in the dairy, beef, pork, and poultry industries;

• Commonly employed in post-stages of transgenesis

• Therapuetic cloning: production of human embryos for use in research. To harvest stem cells that can be used to study human development and to treat disease.

• Organ cloning- type of cloning that does not currently exist but is theoretically possible. With organ cloning, human organs could be grown from a small sample of cells for a specific patient.

references• Transgenesis• http://www.actionbioscience.org/biotech/margawati.html• http://www.nature.com/scitable/topicpage/genetically-modified-organisms-gmos-transgenic-crops-and-732• http://www.wisegeek.com/what-are-transgenic-organisms.htm• Cloning• http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/• http://www.sciencedaily.com/• http://www.ornl.gov/sci/techresources/Human_Genome/elsi/cloning.shtml• http://www.wisegeek.com/what-are-some-benefits-of-cloning.htm