Written Task: Chimerism

Chimerism

Chimerism is a genetical phenomenon suffered by an organism that is composed of two or more different populations of genetically distinct cells, being called chimera or chimaera. Chimeras are forms from different parent cells but emerged from the same zygote, previously combined with another; then, two independent sperms fertilize two different ovules. This condition is either acquired through transplantation or transfusion, or genetical heritage, and allows chimeras to be male, female or hermaphroditic. Chimeras’ phenotypes differences are expressed through skin pigmentation, differential hair growth in opposite sides of the body or eyes of different colours, for instance. However, most of chimeras do not notice they genetically modified condition. Chimerism is presented mostly in animals, even there are plant cases studied separately. 

Hybridism and chimerism are not the same phenomenon: hybrids are formed from the fusion of gametes (a horse sperm and a donkey ovule, for instance) from two different species, which form a single zygote; in contrast, chimeras are produced as two different zygotes are mixed (such as, horse and donkey zygotes).

Marmosets, which share their DNA with the fraternal twins they always give birth to, are an example of chimeras naturally presented. This specific kind of chimerism is called germline chimerism, and is occurred when the germ cells of an organism are not identical to its own. On the other hand, microchimerism is presented through a small number of cells genetically different to its host, as they are originated from another individual. During mammals’ pregnancy, this phenomenon is characterized by a two-way traffic of immune cells trough placenta. Another kind of chimerism is provided by male anglerfishes, which become hermaphroditic as they attach to female individuals, behaving just like a parasite. Male anglerfishes’ body is consumed then by the female’s, developing large testicles. This phenomenon is known as parasitic chimerism.

The audience of this text are people whose biological knowledge is advanced; that is why the text type is scientific report.