Monozygotic [maternal] twins do have the same DNA. Hence they are identical. Genetically identical that is, there are non-genetic variations. Dizygotic [fraternal] twins do not. Fraternal twins can be visually nearly identical, but they are not genetically identical. Clones on the otherhand and have identical nuclear DNA, but are not necessarily identical because some early development processes rely on maternal genome material and not nuclear DNA, and depending on the cloning process they may have different mitochondrial DNA (mtDNA). Matt

-----Original Message----- From: Jim Choate [mailto:ravage@einstein.ssz.com]

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But what about identical sib's. They all have exactly the same DNA!

Actualy identical twins will only share about 50% of their DNA. They get 50% from each parent randomly. This means that only about 25% of the DNA will match their sibling from either parent.

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Or a clone ;).

This of course ignores transcription errors, environment issues, etc. It is possible that even a clone would have protein discrepencies which trace back to DNA strands that end up different than the original source organism. As the organism develops and ages these issues can become quite important. This aspect of DNA matching has gotten the short shift for sure.