Two chimera stories

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.

Sources (including image source):



10 thoughts on “Two chimera stories

  1. Well I am not a person who can comment on Genetics 😛 , but surprisingly I heard of Chimera before! 😯 Out of all places, in the TV serial CSI!!!

    Can’t call TV a idiot box anymore, eh? 😉

    In season 4 or 5 – the episode name was Bloodlines

    In that episode Lindley Parker, a well-dressed pit boss at the Palm Casino, leaves the casino late at night. The scene abruptly shifts a few hours later, when Lindley is running through the forest screaming, her clothes torn. She falls in the road. When the CSIs arrive on the scene, Lindley is still alive. She’s been raped; the CSIs photograph her injuries and send her on to the hospital.

    Grissom finds her car on another road not far away. In the hospital, Lindley tells them that a man ran her off the road. He seemed to be nice at first, but then he attacked her. The DNA the CSIs retrieve matches that from the rape and murder of a young woman named Emma Dobbins that happened a year ago and was never solved.

    The CSIs bring in Todd Coombs, a psychiatrist, as a suspect, based on Lindley’s description of her rapist. She quickly identifies him in the line-up, but he professes his innocence. Shockingly, Todd’s DNA isn’t an exact match for Lindley’s rapist. Greg suggests it may have been a brother of Todd’s who is responsible. When Catherine tells Lindley she identified the wrong man, Lindley quickly becomes angry and insists Todd was the man who raped her. She storms off angrily.

    Todd has four living brothers, and one who died, named Joss. Sara questions fraternal twins Larry and Roger Coombs, who own a car repair shop together. Brass talks to one of the brothers who is a police officer, but the CSIs are unable to locate Kevin Coombs, another brother.

    Meanwhile, Lindley is becoming frantic. She calls Catherine and says she is getting a gun. Catherine tries to talk to her, but suddenly she hears the sound of glass shattering and Lindley screams. The phone goes silent. Catherine races to the casino, where Lindley’s car has just been recovered. There is no trace of Lindley in the car. Nick tracks her cell phone, which is still on, and the CSIs find Lindley in the woods, badly beaten and strangled to death.

    Sara locates Kevin living on the edge of town in a trailer. He is called in for questioning, but the CSIs attention again alights on Todd. A strand of hair was found on Lindley’s jacket, and the DNA is an exact match for Todd. When Grissom examines him, he notices some odd markings on his back.

    Grissom hits the books and reads up on fraternal twins and Chimeras. He brings Todd into the interrogation room: he’s cracked the case. Todd is a Chimera. He should have had a fraternal twin, but the cells of his twin merged back into his, giving him two sets of DNA.

  2. Interesting!

    That’s an example of tetragametic chimera 😀 – in which two fertilized eggs or early embryos fuse together or in simpler words – resorption of one of the fraternal twin by the other while in the womb (vanishing twin)

  3. I dont know if the question im putting up here has anything got to do with chimeras – but still putting it up here –

    If there are two embryos, and after say 3-4 months – one loose the life, can the other still survive??

  4. Yes Anu If one of the twin is miscarried, the other one can still survive. About 1 in 8 pregnancies start out as multiples, but only a single fetus is brought to full term

  5. We are a Tetragametic Chimera, 2 paternal twins, thought we had multiple personality disorder, nope. Didn’t find out until we were in our thirties. As children, people would always say don’t you mean ‘I’ instead of ‘we’. It wasn’t until we fell out of sync that either one of us would notice something was wrong. In our late 20’s we started to developed different but still very close identities. Some made observations that we had sever mood swings. Our mother thought we lost our mind when we told her. Currently learning how to occupy the same space at the same time. Had to learn how to have conversations in our head. For now we take turns driving, while the other sleeps. Have a special tutor lined up to help train us. We are very happy to find each other, but sad that we can’t do things with each other. Course, maybe the tutor will teach us some new tricks. We had 2 girls, and haven’t told them yet. No we are not sterile, which makes us even more rare. We wish to talk with the tutor first. We have checked our daughters eyes and they don’t appear to be Chimera. We’ll check they’re DNA after we tell them. Been telling those who know that they need to buy extra gifts now. 😉 Got divorced some time ago, and we fear complexity in the dating scene as we grow more distinct. We have been thinking of asking our parents to gives us an additional name for Christmas. Very bitter sweet discovery.

  6. It is entirely possible, believe it or not. Kudos to you InnerKiller, for recognizing your differences but being determined to be your true self/selves.

    I am happily married. Keep searching!

  7. Another chimera, here.
    Born most assuredly female, all organs nice and intact; first noticed something was off due to odd markings on skin, extra bones, extra teeth, and blood type abnormalities. (A- and AB- at the same time.) Also, hair and eye issues (one eye is basically colorblind, they are flecked of hazel and brown intermixed) and my hair is blond, gold and brown in bits and pieces. Sort of like a calico cat.

    Distressingly enough, my other half is a brother, so it has caused some rather odd issues.

    It makes for a weird life…

  8. Chimera twins, I heard of this on Discovery Channel, on a show called I’m on my on twin… in the early stages of pregnancy two twin eggs fuse together, and the person has two sets of DNA in their body, like having an unique DNA in the lungs but having different DNA in the hair

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