Nov 30, 2006

have you ever wondered...

What would happen if two pair of identical twins married each other, and then had children? I had this thought while in the shower the other night. It was such a revolutionary thought, I decided to write about it.

Think about it, identical twins have the exact same DNA. So if you take two sets of identical twins, and they marry each other. You have two sets of people with identical DNA. But think about their children! Their children would be, for all intents and purposes, identical to each other as well. Cousins, yet as close as siblings. Would their sons and daughters all look like each other? What do you think? I know this is mind-blowing transitive logic, so just let it simmer and get back to me when you've got something delicious to contribute.

23 comments:

Mike Neilson said...

While I have never considered the scenario you have brought up (certainly it must have happened before), I have wondered about something similar... If identical twins have the same DNA, then how would investigators ever determine (for certain) which twin committed a crime? It seems like if you were a criminal/identical twin, you would be in pretty good shape, given the whole "reasonable doubt" thing. Am I right, or I am missing something obvious here? Also, do identical twins have the same fingerprints? Something tells me that they don't but I really don't know.

In college at my summer job (Quiznos... mmmmm Toasty) I actually worked with these two hillbillies from West Virginia who everyone assumed were brothers. One day the one kid, Teddy, told me that the other kid (Steven)'s father had died. I was really confused, but I later found out that Teddy and Steven had different dads, but the same mom. Nothing too abnormal there, except that the dads were brothers, so these kids were half brothers and half cousins.

Naturally, they looked nearly identical. Gotta love West Virginia.

Mike Neilson said...

By the way, what exactly does one have to search for to get the double-twin picture from Google Images? As always, I am quite impressed with your thoroughgoing research and dedication to your little spot on the web.

Jenny said...

As a student of science, let me let you in on a little concept we in the genetics world refer to as Meoitic Crossing Over. It's kind of a complex and boring concept having to do with the way that chromosomes line up during the second phase of meiosis, the last step before the gametogenesis. I could go on and explain, but I don't think that anyone really wants me to, but I can inequiviacably answer your question and say that the children resulting from the crossing of two identical twins would not be genetically identical. Sorry to ruin your fun little scenario with science, but every party has a pooper, and that's why you brought me.

miss sparks said...

jenny might be my scientific hero...

bex said...

maybe we can just say that the children resulting from the crossing of two identical twins would not be guaranteed to be genetically identical, but leave the possiblity open if all stars and chromosomes were to perfectly line up. that way we can still entertain the idea, and have fun assigning other factors we think might be necessary to make that happen.

Like, I think both of the wives would have had to also eat the #2 value meal from Burger King on the day of conception, sleep on the right hand side of the bed during the whole pregnancy, and have their children on the same day at exactly the same time. Those would be the magical/scientific factors to make sure that the offspring was also identical!

dävid said...

jenny, you didn't ruin the party... that's why i'm friends with you = your scientific acumen. sorry, you thought it was because you were funny, and enjoyable to hang out with. nope. i like to accumulate and collect people based soley on what their gifts offer me.

i'm a friend opportunist.

ok mrs. doctor science. riddle me THIS! Have you ever heard of a thing called a punnet square? not to get all technical on you, but its this square that predicts genetics sort of like a magic eightball. i consulted with it concerning our identical twins scenario, and it told me the kids would look a like.

so... it appears we are at a crossroads.

;)

but you gotta admit, the kids would pretty much look exactly alike.

however, under my same logic that would mean that all children of the same sex born to the same parents would be identical. and i haven't got my field work back yet, but i'm not sure that theory's going to hold water.

Jenny said...

David, I'm warning you. Don't start challenging my scientific knowledge, because I'll break out the answers. And that's a can of worm that nobody wants open. You can ask my students who get stuck in a classroom with me three hours a day.

MF said...

Take her word for it David. PLEASE!!!!

meghann said...

Also the way you come out of the birth canal can affect the shape of your face and stuff like that.
very scientific I know but it's one reason why identical twins aren't always identical looking.

I learned that from Tegan and Sara.

dävid said...

is it pronounced dye-uh-bee-tees or dye-uh-bee-tus?

punnet square y'all.

ashley said...

Do you think the couple on the right would have slightly more attractive children? Clearly they are the better looking couple.

dävid said...

Clearly? Ashley they are identical? It's like saying your reflection is more attractive than you.

wait, i guess there are those "thinning mirrors"

hmm, i go with the couple on the right too.

Anonymous said...

I would also have to agree with Ashley about the couple on the right. While both the men look like young Saddam Husseins, I feel like the one on the left is more of a doufus.

Anonymous said...

I have a friend who's mom's sister married his dad's brother. Genetically speaking, his cousins are just as close as his siblings. They all look quite a bit alike except for the fact that his family has all boys and his cousins are a family of all girls. Too bad this wasn't an identical twin situation or I'd have the perfect answer for you.

mj said...

are they more attractive, or just more alert? lefthand couple looks just a little tryptophan-stoned a la david in the last post (which i just read and it was great).

i would think there would already be a study on this but you must have googled, right?

dävid said...

melissa... just a cursory search. didn't find much.

i must acquiesce to jenny's knowledge. i mean, while i am in my first quarter of my urban planning degree, her 3+ years in molecular physiology ph.d somehow trumps my degree

Mike Neilson said...

don't sell yourself short, david. if you don't plan... urbia... then who will?

Anonymous said...

Ever since "The Shinning" twins freak me out...ESPECIALLY the ones in the old Double Mint Gum commercials. (shutter)

Blythe said...

I lack Jenny's scientific background, but I'm a party pooper anyway. Each conception would be a unique event. There's no way both couples would have the same sperm and same egg get together, out of the millions of possibilities.

And I think the squares show more of the liklihood than anything. Otherwise I would have me some brunette kids.

dävid said...

yeah, blythe... where are these brunette kids you promised me?

dave's genes are like bush's foreign policy.

Iggy Enigma said...

my friend is a twin and always really wanted to do this. but then it didn't work out when his twin got a chick [not a twin] knocked up and they had a shotgun wedding.

looks like i'm party pooper #2

Chris Cherry said...

Even without meiotic recombination, it is statistically improbable that the progeny of the 2 twin pairs will be identical. I digress... ok, so every wild type (normal) person has two copies of every gene in their DNA. A copy of a gene is called an allele. One allele of each gene comes from your mother and the other allele comes from you father. So, let's look at the interesting twins marry twins scenario... Lets pretend that we are looking at gene z in the cousins. Let's say that the mothers of the twins, who are also sisters, have alleles 1 and 2 of gene z (they got them from their parents). Let's say that the Fathers of the cousins, who are also brothers, have alleles 3 and 4 of gene z. Well, during meiosis, which gives rise to germ cells (sperm and egg), you get independent assortment of chromosomes and thus independent assortment of the alleles of gene z. Let's say that cousin 1 inherits allele 1 from mom and allele 3 from dad so cousin 1 is a 1,3 combo for gene z. Now, cousin 2 can also be a 1,3 combo for gene z and this would make the cousins identical (almost - I will explain this part in a minute). However it is just as probable that cousin 2 will be a 1,4 or 2,3 or 2,4 combo for gene z. So simple statistics tells us that the chance that the cousins will be identical for gene z is 1/4 or 25%. On top of this we are not considering meiotic recombination (so astutely pointed out by your scientist friend) which would further decrease the liklihood of the cousins being identical. Also, there is only a 1/4 chance that they will have the same gene z but this is only one gene. It is currently thought that there is somewhere around 40,000 genes in the human genome (in our DNA). So, if we think about that, the liklihood becomes exponentially smaller. However, it isn't as simple as raising 1/4 to the 40,000 power. It isn't going to be that unlikely because you have to consider that when you get a chromosome from one of your parents it comes with thousands of genes and not just one. So, maybe the probability would be 1/4 raised to the 23rd power because we have 23 chromosomes (i am not sure about the math so you should recruit a statistician to your blog). Furthermore, there is another genetic phenomenon called epigenetics which studies the heritable changes in gene expression that don't depend on the sequence of DNA. Now, David I can tell that you are really interested so I will continue. The most applicable aspect of epigenetics to the situation at hand is called genomic imprinting. This is where an allele of a gene can be differentially expressed depending on whether it is inherited from the mother or the father. So although in the slim chance that the mothers and fathers share the same allele of a gene, thus increasing the probability from 25% to 50% of identical cousins, imprinting in fact decreases that 50%. Finally, in females there is a process called x-inactivation where one of the x chromosomes is effectively silenced (also called a barr body). This is also a random process so there is a 50% that female "identical" twins are not completely identical. As a side note, our DNA is being constantly bombarded and mutated so identical twin DNA is not necessarily identical throughout their whole life.

dävid said...

chris, not only do i NOT agree with what you said, but i think you are forgetting some pretty simple rules of human development.

there's these little things called chromosomes... x & y. see, when a man and a woman...

just kidding, i couldn't really carry on that ruse much further. see, the only biological terms i have mastery over are:
biology
cell
chromosome
punnet square