Science Questions

Identical Twins have Identical babies?

Sun, 5th Jul 2009

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Russel Erasmus asked:

If identical twins marry identical twins, will their offspring be identical?


Kat -   This is a really lovely and interesting question.  But the answer is unfortunately, no, but they would be very similar.  So, what happens when you make babies?  What time is it?

Chris -   And how long do we have there?

Kat -   How much detailÖ

Chris -   Be careful.

Kat -   When mommy and daddy love each other very much in a special way, you make babies.  You make babies basically by using half of the chromosomes coming from mom and half of the chromosomes coming from dad and when you create egg and sperm cells in your ovaries and your testes, you kind of get a random assortment of whatever chromosomes you happen to have.  So, half from mom and half from dad, and they come together to make a baby.  And so, this process of random assortment of chromosomes will be going on in both sets of parents to make their children but because heís starting from matching stocks as it were because if you got two identical sets of twins, they have identical sets of chromosomes.  So, itís almost like you just have one set of mom and dadís.  So, the children they produce would not be identical but they would be very similar, as similar as you are to your brothers and sisters because effectively, itís just like having one set of chromosomes that are randomly sorting and going in to babies.  So yes, they wouldnít look identical but they would look very similar.  In some families, brothers and sisters can look incredibly similar.  So, it would just really depend on the luck of the genetic draw.

Chris -   Because identical twins are effectively natureís own natural clones.

Kat -   Natureís clones, yes.

Chris -   And if you wanted to have clones on tap, you should become a nine-banded armadillo because they naturally make quads.  They naturally split their eggs into four identical derivatives which then turn into four genetically identical offspring.  I donít know why, but they make quads, quite naturally that are genetically identical to each other, bizarre.


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Russell Erasmus asked the Naked Scientists: Hi Chris I am a keen listener from South Africa and follow your show on 702. My twelve year old asked me a question which is a bit more in your line of expertise: "....if identical twins marry identical twins and both couples have babies of the same sex will the respective babies be identical..??..." If possible can you answer via this email address to me many thanks Russell Erasmus What do you think? Russell Erasmus, Fri, 19th Dec 2008

With the exception of identical (monozygotic) twins, triplets, etc, each child receives a different mixture of genes from each parent,
(if this were not the case all siblings would be identical).

So the children of one couple would not be identical to the children of the other couple.

Genetically these cousins would be like siblings, so they would be unusually similar cousins, but not identical. RD, Fri, 19th Dec 2008

I think Russell was referring indeed to identical twins... iko, Fri, 19th Dec 2008

Interesting question!  Intuitively, you can see the answer is likely to be "no".  If the answer to your question were an unconditional "yes", wouldn't two brothers always be the same?  We know this isn't true.  You basically have two identical couples each producing offspring, in the situation you describe.  From a genetic standpoint, this is absolutely no different than having one normal couple producing offspring.  This is very important to realize.
Counterpoints, Fri, 19th Dec 2008

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