Question on Cloning

[Sci-Phenomena]

My friend believes that the DNA in say, the skin (or "any" part of a creature) is complete enough to clone the whole creature, I told him thats a load of bull, but I ask sciforums for some real information.

I think it would be a complete waste on the part of any animal that had to have its whole genetic code embedded and copied into every single cell!

 

[Hercules Rockefeller]

I think it would be a complete waste on the part of any animal that had to have its whole genetic code embedded and copied into every single cell!

You are wrong on this point. All the cells of multicellular animals (be they plant or animal) have a nucleus that contains the entire genome (ie. all the chromosomes containing all the DNA) for that organism. As new cells differentiate (ie. mature into their final ‘adult’ form) they deactivate all the genes that are not necessary for their specific function, but they still retain all the chromosomes and the entire DNA. For example, a brain cell retains all the genes necessary for a liver cell, it just doesn’t use them.

(Please don’t anyone bother to argue that this statement is not strictly true by mentioning red blood cells and how mature RBC’s do not have a nucleus! We can ignore rare exceptions for the purposes of this question...)

My friend believes that the DNA in say, the skin (or "any" part of a creature) is complete enough to clone the whole creature, I told him thats a load of bull, but I ask sciforums for some real information.

You are only semi-wrong on this point. In theory, any cell can be used to clone a new animal by nuclear transfer because, as I have just said, every cell contains the entire genome for that animal. In practice, we don’t know if any cell can be used. For a start, there are a large number of different types of cell in a large complex animal such as a mammal. It is hard to imagine that science will ever manage to work its way through every cell type such that it can be definitely concluded that it is capable with all types of cell. Also, cloning new animals appears to be much easier using cells associated with the sexual organs/gonads. In other words, cells from the testes or the ovary seem to work much better than somatic cells (ie. all the cells of the body other than the reproductive cells). But, somatic cells of various types have been used to clone animals. Dolly was cloned from a mammary cell, and I believe that skin cells have been used successfully. So we know for sure that it is possible to use somatic cells.

Of course, cloning new plants from any cutting of another plant is easy. This is one of the amazing differences between plant and animal genomes – plant cells have an amazing ability to de-differentiate into precursor cells by activating long dormant “embryonic genes”, then re-differentiate to form a new plant. Most animal cells cannot come close to achieving this.

Take home message: you totally lost this bet!

 

[Blue_UK]

(Further to what HR has said)

In fact, your friend is doubly right - each cell has two copies of the genome! (bar sperm and egg cells, which have only one and combine to create a full set of two).

 

[Sci-Phenomena]

Yes, I have lost THIS arguement, very interesting information

 

[spuriousmonkey]

My friend believes that the DNA in say, the skin (or "any" part of a creature) is complete enough to clone the whole creature, I told him thats a load of bull, but I ask sciforums for some real information.

The DNA might be complete, but it also might be in the wrong configuration. It might be methylated in the wrong places.

In theory all the DNA is there, but there is more to nuclear DNA than just DNA. So he was right and he was wrong at the same time. Because DNA alone isn't the complete story. How it is organized makes it competible for cloning. This results that not all cell types are suitable for cloning, and also the age of the cells can matter. A particular skin cell might be ok for cloning in a young animal and totally unsuited in an old animal.

 

[invert_nexus]

And don't forget the importance of the physical makeup of the cell itself.

People tend to concentrate on the DNA as if it were the master control of the cell, and it is in many ways, but the physical constitution of the cell is also important.

That is, the proteins which are expressed in the cell. The matrix into which the cell is embedded and so on.

Yes. These things are derived ultimately from DNA as proteins come from expression of DNA. But, the important thing to consider is that there is no point at which DNA exists sans cell. DNA doesn't build the cell from scratch, rather it exists in an environment which is conducive to its function.

It is this environment which feeds back to the DNA and determines which aspects of the DNA are expressed. Determines which segments are methylated (and various other control mechanisms and tags).

This is seen most clearly when one considers mitochondria's maternal inheritance. That's because the cell is inherited from the female. From the egg. The cellular machinery is derived from the egg.



On another note, let's say we're dealing with a female clone. What happens with that extra X chromosome? One X chromosome is randomly inactivated during development. Does it need to be reactivated again for cloning? And what does this mean when it is again deactivated? Is it random again? That means that the OTHER X chromosome might be expressed in the clone? Does this mean that female clones only have a 50/50 chance of being identical in genetic expression?

 

[invert_nexus]

And while I'm thinking about protein content of germ line cells....

Where do the proteins come from in an egg and sperm? Do they come from the DNA of the cell or are they inherited somehow? Are germ line cells with only half the genetic content able to function well enough for protein manufacture and such?