Twins intermediate between identical and fraternal discovered
For those who are not familiar with the term ‘Chimera’ – A person who is a chimera has two or more genetically different cells coming from different zygotes.
A chimera can be formed in either of the following two ways:
1. From four parent cells – Two fertilized eggs or early embryos fuse together
2. From three parent cells – A fertilized egg is fused with an unfertilized egg or a fertilized egg is fused with an extra sperm
We all know that there are identical twins and non-identical or fraternal twins. Now an instance of ‘semi-identical’ twins has come up.
This is the first time that a case of ‘semi-identical’ twins has been reported. This is a case of three-parent cells fusion in which two sperm cells fuse with a single egg which makes the twins chimeras. So, here the twins are identical through their mother’s side, but share only half their genes on their father’s side.
According to geneticist Vivienne Souter, of the Banner Good Samaritan Medical Center in Phoenix, Arizona:
“Their similarity is somewhere between identical and fraternal twins.”
This case came to the notice of Souter and her colleagues while they were investigating one of the twins’ genetic makeup, who was born with ambiguous genitalia.
Formation of chimera is a rare occurrence in itself. This ‘double-fertilization’ due to fusion of a single egg by two sperms is thought to happen in about only 1% of human conceptions. But, the subsequent twinning of chimeras may be the rarest of the rare.
According to news@nature
“Their existence and discovery relies on three unusual, and possibly unlinked, events: first, that an egg fertilized by two sperm develops into a viable embryo; second, that this embryo splits to form twins; and third, that the children come to the attention of science.”
The twins were conceived and born normally and their growth and mental abilities appear normal. It is really astonishing to hear that the twins still came out to be healthy after being conceived through this rare, complicated and almost impossible process.
15 per cent-human sheep
Now another instance of Chimera…this time – closer to the origin of the word ‘Chimera’ which comes from a creature in Greek mythology that had body parts from a goat, a lion and a serpent. Well not exactly…
Here goes the way that mythological character looks like 😀
Scientists have successfully created a human – sheep chimera, which has the body of a sheep and partial human organs for the first time
The purpose of the creation of these chimeras, which has 15 per cent human cells and 85 percent animal cells, is to create organs which contain large proportion of human cells for subsequent transplantation into human bodies.
This technique, perfected by Professor Esmail Zanjani, of the University of Nevada, involves injection of adult human cells into foetus of a sheep.
Though this human-sheep chimera has been created with an intention of saving human lives, it is likely to meet criticisms about scientist playing with natural creation and also the possibility of introducing silent animal viruses in human body (which are harmless for animal, but may be threat for humans).
Dr Patrick Dixon, an international lecturer on biological trends, warned:
“Many silent viruses could create a biological nightmare in humans. Mutant animal viruses are a real threat, as we have seen with HIV.”
There is also a fear that this process could end up creating a hybrid with the features and characteristics of both man and sheep.
But Prof Zanjani refuted this :
“Transplanting the cells into foetal sheep at this early stage does not result in fusion at all.”
Read more about this here.
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