What is the difference between a Chimera and a Transgenic?

Question

I was reading on the bbc news website that the laws regarding IVF treatment has changed and as part of this, creation of "Chimeras" - a creature that is made from a mix of human and animal DNA - is banned. However, Transgenics are animals that contain human DNA. IS the difference simply that in transgenics, the DNA is inserted after fertilisation, rather than having the genes spliced? If anyone knows, I would be more than greatful to be enlightened.

Answer 1

Transgenesis involves transfer of foreign DNA into totipotent or pluripotent embryo cells (either fertilized oocytes, cells of the very early embryo or cultured embryonic stem cells) followed by insertion of the transferred DNA into host chromosomes. One method that allows foreign DNA to integrate into the chromosomes of the target cells uses retroviruses, RNA viruses which naturally undergo an intermediate DNA form prior to integrating into cellular genomes. If the foreign DNA integrates into the chromosomes of a fertilized oocyte, the developing animal will be fully transgenic since all nucleated cells in the animal should contain the transgene. If chromosomal integration occurs later, at a postzygotic stage, the animal will be a mosaic, with some cells containing the transgene and some others lacking it. If the transgene is present in germline cells it can be passed through sperm or egg cells into some of the animal's progeny, and PCR-based tests can be used to quickly screen for the presence of the transgene. Progeny that are transgene positive can be expected to be fully transgenic; all their cells should have developed from a fertilized oocyte containing the transgene.

Chimera an organism derived from more than one zygote into a single embryo, which are usually all normal but genetically distinct.

An example of usage of chimeras, involves transferring the foreign DNA initially into cultured embryonic stem (ES) cells. Mouse ES cells are derived from 3.5–4.5 day postcoitum embryos and arise from the inner cell mass of the blastocyst (. The ES cells can be cultured in vitro and retain the potential to contribute extensively to all of the tissues of a mouse, including the germline, when injected back into a host blastocyst and reimplanted in a pseudopregnant mouse.

The developing embryo is a chimera: it contains two populations of cells derived from different zygotes, those of the blastocyst and the implanted ES cells. If the two strains of cells are derived from mice with different coat colors, chimeric offspring can easily be identified. Use of genetically modified ES cells results in a partially transgenic mouse.

Answer 2

genetically speaking a chimera is like the greek mitology animal, or a cross between 2 species that can never reproduce (eg a dog with the paws of a cat) transgeneic is instead an animal that has foreign proteins (usually just a few) and in appearance is exactly the same as it would be without the foreign dna inserted. usually transgenic is made to withstand some bad environments like bacteria that are able to produce human insulin (used in medicine) due to a piece of human insulin gene inserted in them. the difference in what you say is to avoid improving the human race like making babies that are more resistant to diseases without an actual study behind but just addying foreign dna from animals. the problem they are addressing here is not the fact that they introduce foreign dna into a human but the long term consequences that this would have on the person (think about it and you will come with your own explanation)

Answer 3

Chimera is which has two genetically distinct kinds of cells which originate from at least 2 different zygotes (fertilized eggs). Those zygotes can be from different species.
Chimeras are also different from hybrids. A mule would be a hybrid of a horse and a donkey and a sperm and and egg cell from two different species form a single zygote.
A chimera for example could be a pig which has a human liver/ liver cells.
A transgenic animal is a animal in which all the cells contain the same genetic information. But in addition to the original genetic information it contains genetic information for e.g. a certain human protein. A useful application of this is the production of human insulin by bacteria (see last link).
The wikipedia links will provide you with more detailed information.

Answer 4

If you have an interest in this sort of thing then I recommend you read Michael Crichton's new book 'Next'. I just finished it yesterday and it is about the near future in genetics and explains a lot of these terms at the same time as telling a great story.