May 20, 2005

Hard Question

For any of you out there in science land. This whole cloning thing is so rife with polite euphemisms in the press (wouldn't want to panic the little people, now, would we) that I cannot exactly figure out what the hell is going on. My inner nutbar conspiracy theorist jumps up and down at that, shrieking "Of course! THEY want your ignorance!" and I am tired of beating him into submission with a tire iron. SO...

Can anyone explain exactly HOW we get from "female egg" and "skin cells" to "blastocyst" which, if I recall my college biology correctly is an early stage human being, simply by "stimulation?"

The article I read in the WSJ made it sound as though adding material from the skin cells to the egg and then magically stimulating it had the same effect as fertilizing the egg with a sperm. What the hell? That can't be right! Unless "stimulating" is some weird euphemism for "fertilizing." In which case I want to euphemize me some dumbass reporters.

Seriously. I don't get that at all. Are the eggs pre-fertilized, as in, are they frozen embryos? That would make more sense, but that isn't what the article stated.


Posted by Big Arm Woman at May 20, 2005 01:43 PM

"parthenogenesis [Gr.,=virgin birth], in biology, a form of reproduction in which the ovum develops into a new individual without fertilization. Natural parthenogenesis has been observed in many lower animals (it is characteristic of the rotifers), especially insects, e.g., the aphid. In many social insects, such as the honeybee and the ant, the unfertilized eggs give rise to the male drones and the fertilized eggs to the female workers and queens. The phenomenon of parthenogenesis was discovered in the 18th cent. by Charles Bonnet. In 1900, Jacques Loeb accomplished the first clear case of artificial parthenogenesis when he pricked unfertilized frog eggs with a needle and found that in some cases normal embryonic development ensued. Artificial parthenogenesis has since been achieved in almost all major groups of animals, although it usually results in incomplete and abnormal development. Numerous mechanical and chemical agents have been used to stimulate unfertilized eggs. In 1936, Gregory Pincus induced parthenogenesis in mammalian (rabbit) eggs by temperature change and chemical agents. No successful experiments with human parthenogenesis have been reported. The phenomenon is rarer among plants (where it is called parthenocarpy) than among animals. Unusual patterns of heredity can occur in parthenogenetic organisms. For example, offspring produced by some types are identical in all inherited respects to the mother."

You're welcome.

Posted by: Laura at May 20, 2005 01:54 PM

I don't think they were fertilized. They take the genetic material out of the egg, replacing it with the genetic material from the skin cell and then "stimulate" the egg with chemicals, provoking it to start dividing, tricking the egg into believing it was fertilized the old fashion way.

But, it is a developing baby, a clone, an embryo once the process starts. It's just that with all that manipulation it unlikely the baby would develop "normally."

Posted by: bigdocmcd at May 20, 2005 01:57 PM

As I understand it, the nucleus of the ovum is removed and the nucleus of the skin cell put in its place. The result is an egg cell with the DNA of the person from whom the skin cell came. (The mitochondrial DNA will be different, because the mitochondria sort of come with the ovum as a package deal, but otherwise you have an ovum with the genetic characteristics of the person you took the skin cells from.)

I don't know about the "stimulation." I imagine it means replicating the chemical environment of a uterus so that the thing starts dividing.

Posted by: Michelle Dulak Thomson at May 20, 2005 02:07 PM



Posted by: BAW at May 20, 2005 02:41 PM

I don' know nuttin 'bout clonin' no babies, Miss Scahlet...

Posted by: snopercod at May 20, 2005 07:52 PM

All I know is that those bastards killed all the jedi.

Michelle's right, it's just taking the genes from your skin cell and putting it into the egg.

Posted by: Sam at May 23, 2005 09:42 AM

Michelle's right; that's the deal. The egg is often stimulated with a small electrical shock, which has a similar effect to sperm entry (which is what normally triggers a zygote to start dividing.)

In addition to the mitochondria issue, there'a also a question about genetic "imprinting", which can be screwed up in clones. Basically, some genes are turned "off" if they are from the egg, and others if they are from the sperm. Switches are reset during the fertilization process. Since the nucleus in a cloned egg didn't get built the normal way, the switches can be set wrong, producing too much or too little of a protein. This can have significant side effects.

Posted by: Dictyranger at May 24, 2005 08:22 AM

Wow, two comments in a row beginning "Michelle's right." Do keep saying that, please; it happens so seldom ;-)

Dictyranger, thanks for the info on "stimulation" and "imprinting." I didn't know about either.

Posted by: Michelle Dulak Thomson at May 24, 2005 04:42 PM

Michelle's right, it does happen so seldom!

Sorry. Sorry. I just couldn't resist. I'm sure it actually happens all the time.


Posted by: Wince and Nod at May 25, 2005 02:41 PM


Bless you ;-)


Posted by: Michelle Dulak Thomson at May 25, 2005 04:51 PM