Fascinating Concept!Polar Body Twinning-Half Identical Twins

observer

Thu, Jan 12 2012, 6:12 pm

I wasn't sure which section to put this in, so here goes.

I recently came across the concept of "Polar body twinning" and I found it fascinating. Basically, the egg splits before fertilization, and two separate sperm fertilize the two parts. So they are identical from their mother's DNA and non-identical from the father, and it can even be a boy and a girl. They would obviously look more alike than fraternal twins, as they are half identical. The bolded is some more info:

Quote:

Identical -- monozygotic (one zygote) -- twins form when a single fertilized egg splits into two genetically identical parts. The twins share the same DNA set, thus they may share many similar attributes. However, since physical appearance is influenced by environmental factors and not just genetics, identical twins can actually look very different. Identical twins are always same-relations sets.

Fraternal -- or dizygotic (two zygotes) -- twins develop when two separate eggs are fertilized and implant in the uterus. The genetic connection is no more or less the same as siblings born at separate times. They may look alike, or they may not.

Scientists have theorized a third, hybrid type called polar body twinning, that occurs when an unfertilized egg splits into two parts and each part is fertilized by a different sperm. The twins would then share one-half of their gene set (from their mother). Because it is the father's DNA that determines the relations, the twins can be either same-relations or male/female.

So I've been thinking about this concept, as it really is fascinating and can also show a lot about genes. I was wondering if anyone else has come across this concept and knows more about the topic.

And my main question is: Is this just a theory? Or has it ever happened? I'd love to hear other people's opinions on this!

chavamom

Thu, Jan 12 2012, 6:24 pm

I'm confused on how this would work exactly. A fertilized egg is "programmed" to split and divide. An unfertilized egg is not. Hmm. I'm not sure how it would divide without the DNA splitting.
I'm going to vote theory but would be interesting if they figure out that it can happen.

veganesther

Thu, Jan 12 2012, 6:25 pm

this seems unlikey b/c the egg before fert. only contains 1/2 the dna of a human being. what would cause a half cell to replicate dna and then split?
No other cell in the body under goes replication w/o a full set of chromosomes.

chavamom

Thu, Jan 12 2012, 6:30 pm

veganesther wrote:

Right. You said what I meant but said it more clearly.

observer

Thu, Jan 12 2012, 6:47 pm

When I was reading up on it, what I came across seemed to indicate that the egg leaves behind a polar body (kind of like the shell of the egg or something like that) which contains the same genetic material as the egg, and that is what gets fertilized. So it may not be the egg splitting literally.

I also think this is mainly theory, but I wonder what would come out in the future.

veganesther

Thu, Jan 12 2012, 6:57 pm

I was taught in biology class that the polar bodies' purpose is to nourish the yet to be fertilized egg and to keep the soon to be fertilized egg "company". I believe the polar body's cell membrane is impervious to sperm, otherwise there would be lots of twins all the time. because all eggs have polar body buddies.

yksraya

Thu, Jan 12 2012, 8:07 pm

that's a very wild theory. fraternal twins can look alike just like any other sister /brother in every family. I personally think scientists are way too crazy.

mommy27

Thu, Jan 12 2012, 9:00 pm

I think the egg and the 3 polar bodies are the result of meiosis, in which case they would all be at least slightly different in their DNA if not majorly, both in which chromosomes they have (from paternal and maternal origins) and from crossing over, so you wouldn't have half identical twins anyway, even if it were possible to have a polar body get fertilized.

imamiri

Thu, Jan 12 2012, 9:04 pm

yksraya wrote:

that's a very wild theory. fraternal twins can look alike just like any other sister /brother in every family. I personally think scientists are way too crazy.

If it weren't for "crazy" scientists, we would still think the earth is flat and nothing of germ theory, etc.

mommy27

Thu, Jan 12 2012, 9:06 pm

We also don't know where she quoted it from. These scientists could be anybody and plus we only know the real difference between fraternal and identical twins from scientists in the first place!

imamiri

Thu, Jan 12 2012, 9:18 pm

mommy27 wrote:

We also don't know where she quoted it from. These scientists could be anybody and plus we only know the real difference between fraternal and identical twins from scientists in the first place!

There are a few medical journals online that are about polar twins and the possibility of.

HindaRochel

Fri, Jan 13 2012, 2:26 am

When the egg matures it splits into two; one a polar body, the other the egg which is ready to be fertilized.
The idea is that somehow the polar body goes on to become fertilized, not that the polar body splits.