Thank you, Islam Saadeldin, for such an interesting question. 

I look forward to reading the inumerous interesting comments that your question arises.

The latest issue of National Geographic (Nov. 2014) brought an article with a good collection of photos, that might interest this issue. 

http://www.nationalgeographic-magazine.com/eu-29/current-issue/

(«Real Zombies - The Strange Science of the Living Dead»)

As an Anatomist, I have developped some interest on the figure of the Chimera, weich, to me, is the symbol of transplantation and graftingm, in general terms.

I find that, throught the times, you can find traces of medical atempts to develop grafting, in every culture in which you find symbolic representations of zoo-anthropomorfic figures, as you may read in this article that might interest you:

 https://www.researchgate.net/publication/266392790_Anatomy_and_Grfts_From_Ancient_Myths_to_Modern_Reality

Hope this was useful.

Kind regards from Portugal! Maria

Article Anatomy and Grfts, From Ancient Myths to Modern Reality

Thank you Prof. Maria for this useful information and the interested article. 

Dear Islam,

I want to share my knowledge about chimeria. It can be seen in human and other animals in nature. In early stage of gestation blastomers from two different embryos can unite and create a baby. As you can predict there are two different genetical material in all tissues (brain, skin, kidney etc.). So this people is identified by symetrical sing on back or some part their body. Because the cells of skin from two different genetical material have different melatonine concentrations. However, I do not have any information about incidence of this fact. Nevertheless, chimeric incidence in some animals may be high especially cat, pig, dog etc. 

Thanks Prof Umut, it is the first time to know that!!

I searched and found that there were more than 4 reported cases of human Chimera occurred naturally!!

Ballantyne KN, Kayser M, Grootegoed JA , 'Sex and gender issues in competitive sports: investigation of a historical case leads to a new viewpoint', British Journal of Sports Medicine. (May 2011) doi:10.1136/bjsm.2010.082552

Bowley, C. C.; Ann M. Hutchison; Joan S. Thompson; Ruth Sanger (July 11, 1953). "A human blood-group chimera". British Medical Journal: 81.

Strain, Lisa; John C.S. Dean; Mark P. R. Hamilton; David T. Bonthron (1998). "A True Hermaphrodite Chimera Resulting from Embryo Amalgamation after in Vitro Fertilization". The New England Journal of Medicine 338: 166–169.

"She's Her Own Twin - ABC News". Abcnews.go.com. August 15, 2006. 

Dear Islam,

Chimerism also occurs naturally in cattle, when there are twin calves.  In these cases the blood supplies of the developing twins can link, and hematapoetic stem cells are shared, so the calves have blood cells from two different lineages.  This contributes to the look and phenotype of freemartin cattle (along with the sharing of testosterone from the male twin), where the female freemartin has abnormal reproductive development.

Experimental chimerism is used as a tool, usually to help get a desirable genetic component back into a breeding population of animals.  For example, I might want to see what genetic changes are necessary to repair a mutant gene causing cystic fibrosis in mice.  I can make genetic changes to mouse cells in a petri dish, but I have to incorporate those changed cells back into a whole animal to see if it worked.  So I make my gene changes to mouse embryonic stem cells in the lab, then combine the cells with a developing mouse blastula, put the embryo back into a pregnant mother, and the pup that is born (if I am lucky) will be made of cells from the host line and cells from the genetically altered donor line, and so is a chimera.  When the mouse is an adult it will produce some gametes (eggs or sperm) that are from the host lineage, and some that are from the donor lineage.  Any offspring fertilized from sperm with the 'fixed' gene will be normal, non-chimeric mice with the altered genetics, and you can check to see the effect of the genetic change.

In some of my old research, we worked to see if chimerism could be used as a conservation tool in fish.  Fish eggs and fertilized fish embryos of rare species cannot be cryopreserved, because the fatty yolk interferes.  But one can freeze and cryopreserve the isolated blastomeres from early embryos.  To get those stored blastomeres back into a breeding animal, one can thaw them and add them to a developing fish embryo, making a chimera.  The chimera can then breed, passing the recovered genes into the population.

Hope this helps,

Eric

Thanks Prof. Eric Nilsson for these useful information. 

Contribution of stem cells to chimeras is also the ultimate proof of pluripotency (e.g. when injected into a mouse blastula).

Also chimerism is a very important tool in developmental research to investigate the functions of several factors such as Cdx2, Oct4, Gata 3/4.

I believe you talk about transgenic animals.

Transgenic animals are important as part of non-clinical research of specie specific biotechnological products:  both to understand the internal relation between cytokines and other  mediators and the mechanistic activities of drug.

Transgenic mouse have contributed to understand activities of genes, confirm its relation with human genetic disease and confirm pharmacodynamics effect of gene therapy and other products.

Knockout-Transgenic Mouse as Model of several human disease are invaluable tool to reduce time between lab researches to patient of novel biotech drugs.

There are special ethical considerations about care and manipulation of these type of animals. They are included in legal bodies as mandatory requirements.

i hope help you

Dear Colleagues,

I would like to share the latest Nature article about Chimera;

http://www.nature.com/nature/journal/v540/n7631/full/nature20573.html

Best regards.

Islam

The human animal chimeras would be quite useful in understanding many diseases and disorders where we are still unable to have a precise animal model. For an example; human brain remains to explore for its complex structure and functions (real time) and we do not have a complete replica of the human brain in vitro. Here we need these chimeras developed for desired tissue and organs. 

Second, if we consider many infections such as Malaria, H1N1, MTB and HIV, all these infectious agents evolved with the precise host to complete their life cycle. Now, we can not simply go for any animal model to study life cycle and molecular biology associated with such infection. Here also we need a selective tissue/organ and hence chimera. 

I hope I  made myself clear 

Chimera occurs in un identical twins also this can be inherited as well as translated from other persons through blood or organs translation so , it happened with a dipped rate.