Explain a Chimera

I keep reading it’s not a hybrid like a Mule, but then what is it? I find it confusing. A classic example is a geep or goat crossed with a sheep, but then I read that a goat and sheep can’t mate

Can someone explain this in simple language?

It’s not a hybrid with an egg and sperm from different species, but a blending of two individuals (whether the same or different species). Think of it as a reverse identical twin-- some time during the early development stage of two embryos, they fuse together and form one individual. Cells in one part of the body will come from one of the original individuals and other parts of the body from the other individual.

Wikipedia is always a good place to start. Chimera.

A good show about this runs on The Learning Channel once in a while. It’s called “I am my own Twin”.

The chimera was a legendary animal from Greek mythology that had the head of a lion, the body of a goat, and the tail of a dragon (or some variation on this depending on what legend you read).

The modern chimera is exactly what John Mace said above, it’s a fusing of two different DNA sets into a single person (or animal). It was once thought to be extremely rare, but DNA testing has shown that it occurs a lot more often than people once thought, but just often occurs without any visible symptoms.

Normally, a person has just one set of DNA, which is formed by a combination of your mother’s and father’s DNA. In a chimera, you get two different sets of DNA, formed by two non-identical twins fusing into a single person. Since you have multiple “things” combined into one person, it is named after the legendary chimera, which was a combination of different animals all in one.

Most of the time a chimera isn’t really noticeable. However, you can have weird things like lighter hair or skin on parts of your body and darker hair on other parts. In the most extreme cases, you have DNA that makes you both male and female, and you end up with both sets of sexual body parts.

A mule is formed by a donkey and a horse, and even though it has two different parents, it ends up with one set of DNA. It’s a mule from one end to the other.

Good question.
Great answers.
Ignorance fought!

Do Chang and Eng count?

No. Besides, they originated from one zygote, so even if they fully merged at an earlier stage, they wouldn’t be a chimera. All the DNA in the cells of the merged individual would be the same.

All right, then how about that fellow in India who partially reabsorbed his twin in utero (let’s say for the case of argument that it was a fraternal twin, instead of an identical one)? How do we define individual, in these cases?

As a semantic matter, I would say no since that is called “parasitic twin”. But many things involving living organism do not have distinct boundaries, so that might be considered one extreme end of the spectrum, as the merging of two individuals can occur at many points during the development process.

A true chimera will be “splotchy”, with some parts having one set of genes, and some the other, all over the organism. But it’ll still have the normal total number of each part.

Not necessarily. If you read the wikipedia article, you’ll note that there are different types of chimeras. You are describing only what is referred to as “tetragametic chimerism”, but there are other kinds as well. It’s probably true that most people are thinking of tetragemetic chimeras when they use that term, though. (Other than the mythical type, that is.)

Sheep and goats mate with great regularity. Any time you put a rutting billy in with a ewe mating will occur.
What is less common is the production of offspring, although even this has been documented on very rare occasions.

So a human chimera would have 92 chromosomes? I didn’t think this was possible.

They will have 46 chromosomes in *each cell *(except blood platelets of course), but a different set of 46 for one line of cells compared to those in the other line so 92 different ones overall.

My apologies if this is a hijack:

My 94 year old grandmother has one blue eye and one brown eye. I understand that this is a sign of a chimera.

1.) How likely is it that she is a chimera?
2.) Is there any benefit to scientists checking her out?
3.) If so, how invasive will this “checking out” be?

I’m all for the advancement of science, but I don’t want my grandmother to suffer unnecessarily.

Thanks,

I don’t know how likely it is that your grandmother is a chimera, but eyes of a different color can be caused by a lot of things. David Bowie, for example, has two different colored eyes as a result of a fight he had when he was young.

Some smart guy says here that it is “frequently genetic in origin” but doesn’t give any details: http://www.straightdope.com/classics/a971205.html

There’s more info here: http://www.sciam.com/askexpert_question.cfm?articleID=00015D35-7293-1C71-9EB7809EC588F2D7&catID=3&topicID=12

It isn’t. It is more often a sign of eye damage. It woudl be highly unlikely for a chimera to develop in a pattern that produced different eyes. Normal partitioning for chimaera is longitudinal, not lateral. IOW the head may be different from the hands, but it’s highly unlikely that the two sides of the head would be different.

It’s got the head of a lion, the middle (and sometimes the second head) of a goat, and a snake for a tail. Bellerophon killed it by peppering it with arrows while flying out of reach on Pegasus’ back, then shoved a lump of lead down its throat that got melted by its own fiery breath.


What?

(I suggested ann interesting take on its origin in my book)
It’s also, I see on an internet search, the name of a lingerie company (!!) The internet is so educational

http://www.chimeralingerie.com/

So how can I make this the hook on my soon-to-be-written best-seller crime fiction thriller? Does the suspect’s DNA found at the crime scene differ from the DNA harvested at the court-ordered test? By how much? Could the canny medical examiner (you know, the one who gets DNA results in 2 minutes) say, “Nope, it’s not a match,” or would he say, “This DNA is from two closely related individuals?” (Or even, “Sergeant, you’ve got a rapist-murderer chimera on your hands!”)

To my understanding, there is a 1/N chance of detecting different DNA, where N is the number of original zygotes (often 2). So if the DNA analyst is not expecting a chimera then there’s a 50/50 chance that the results would not match. In real life this was actually an issue in a custody case where a woman claimed she was the mother of a child but the initial test showed otherwise. After repeated test, a match came up, leaving everyone to wonder what the hell happened in the first tests, and to everyone’s surprise, it turned out that the mother was a chimera.