Identical twins have the same genetic make up but they differ in development so are they in a way clones?

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    $\begingroup$ I don't see the point of your question. Seems like an unnecessary debate on the semantics. Lets say if we clone you, it is not really necessary that your clone will behave like you. There can be developmental differences too. Will that make the clone of you actually "not a clone" of you? In any case, in professional references people hardly use the word "clone" to mean genetically identical. The usage of the term "cloning" in molecular biology and developmental biology is restricted to certain procedures. $\endgroup$
    Commented Mar 21, 2016 at 17:01
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    $\begingroup$ I'm voting to close this question as off-topic because OP basically asks what a clone is. Too trivial imo. $\endgroup$
    – AliceD
    Commented Mar 21, 2016 at 20:02

2 Answers 2


Are identical twins clones?

A clone is an individual that is genetically identical to another (see wikipedia > cloning). As you said, identical twins (better called monozygotic twins) are genetically identical to one another and therefore an identical twin is a clone indeed.

The role of the environment

Be careful, to not think of clone (incl. monozygotic twin) as individuals that look exactly alike or behave exactly alike. Even for traits that are highly heritable, environmental variation is causing a lot of phenotypic variation and two monozygotic twins do not encounter the exact same environment and can eventually grow up to be very different people. Note that the two blastulas will differ a little bit in concentration of proteins, fats, developmental factors and other things. Such small differences can have important impact on the development of the fetus.

See this post on heritability to have a better understanding of the underlying environmental variation explaining phenotypic variation in populations.

But they are clone for life, right?

Well, it depends on the exact definition of clone but it is important to understand that the expression of genes varies a lot in response to the environment. See for example wikipedia > epigenetics. Also genes may change slightly as we age (see Can genes change as we age?).

  • $\begingroup$ The same wikipedia article you quote clearly states that twins are not clones (see my edited answer) $\endgroup$
    – Thawn
    Commented Mar 21, 2016 at 19:00
  • $\begingroup$ The article says Human cloning is the creation of a genetically identical copy of a human [..] It does not refer to the natural conception and delivery of identical twins This claim is about the expression human cloning and not about what a clone is. $\endgroup$
    – Remi.b
    Commented Mar 21, 2016 at 19:15
  • $\begingroup$ What is wrong with using the definition for human cloning? The question clearly refers to humans. However, even if you would like to be picky: I think to such a general question, the more generally used and clear definition given by merriam webster applies much better than stretching the technical definition normally used for bacteria and apply it to humans. $\endgroup$
    – Thawn
    Commented Mar 21, 2016 at 20:04
  • $\begingroup$ As I understand it, the term human cloning refers to a set of processes to create clones. Generally, this set of processes does not include monozygotic twins. This does not mean that identical twins are not clones of each other. A clone is generally defined as an organism that is genetically identical to another one. In this regard, two monozygotic twins are clones. Does it make sense? $\endgroup$
    – Remi.b
    Commented Mar 21, 2016 at 20:14
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    $\begingroup$ It would be great IMO, if one of us could offer an answer who draws to the issue behind the definition of clone (and eventually cloning) and how this relate to monozygotic twin. It will be important to make clear that, monozygotic twins, just like clones, are genetically identical. $\endgroup$
    – Remi.b
    Commented Mar 21, 2016 at 20:18

Simple answer: No.

Merriam webster defines a clone as follows:

a plant or animal that is grown from one cell of its parent and that has exactly the same genes as its parent.

Identical twins have identical genes to their sibling not their parent. The reason behind this is that this definition of cloning refers to the artificial biotechnical method of creating genetically identical offspring. While identical twins are a naturally occurring phenomenon caused by a splitting of the embryo during early development.


Long answer: It depends entirely on how you define a clone.

On one hand there is the original (biological science) definition (used in Remi's answer) which is mostly applied to bacteria: In that definition, clones are distinct organisms with identical DNA information. In that definition, identical twins are indeed clones, since they share the same DNA information.

On the other hand there is the definition from Merriam Webser (quoted above) which is the nowadays more commonly used definition outside the scientific community (also depicted in popular movies like Star Wars). That definition refers to the technical process of "human cloning" which is defined in the The wikipedia article that Remi quoted:

Human cloning is the creation of a genetically identical copy of a human. The term is generally used to refer to artificial human cloning, which is the reproduction of human cells and tissues. It does not refer to the natural conception and delivery of identical twins.

According to that definition, identical twins clearly are not clones and they would probably be offended to be called such.


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