During conventional reproduction, a child recieves half it's DNA from each parent. This may include many "undesirable" genes as well as some recessive lethal genes. Every mammal has two copies of all the DNA, one copy from each parent. Recessive genes are those that only affect the organism's metabolism when there are two copies present.

The recent cloning of sheep indicates that Human cloning is quite possible. Cloning does not produce a full grown sheep (or human) when it is done. It produces a fertilized egg with DNA identical to the parent. The source of the DNA is a parental "cell line". Some mammalian cells can be kept alive as cell cultures, even when seperated from the rest of the organism. It is the nucleus of a cell in a cell culture, which contains all the DNA, that ultimately replaces the nucleus of an egg cell during cloning.

Recessive lethal genes are genes that will prevent an organism from surviving if it has two copies of the lethal gene. When this occurs, the developing organism is usually spontaneously aborted early on. I've heard estimates that the average person has a single copy of 7 different recessive lethal genes.

Conventional genetic manipulations of mammalian cells, known as gene targeting, can replace one gene with another in a cell line. Defective and/or undesirable genes can be replaced one by one. This is time consuming and difficult, but it is currently done on a regular basis with mammalian cells. Prior to cloning, a corrected cell line could only be grown into a whole organism in a few rare cases. Cloning of the repaired cell line is now possible, but there are still many possible problems to overcome. Aside from having the defects corrected, the child organism is identical to the parent.

An embryo that was spontaneously aborted could be repaired if the problem was recessive lethal mutations, and not some other kind of developmental error. Although errors may have occured in development the first time, the cells may still survive as a cell line. This cell line, once the lethal mutations are corrected, might then begin again as a repaired clone. It isn't necessary to stop at simply repairing the lethal genes. Any desired traits that have been defined genetically can just as easily be substituted into the cell line creating "super cells".

This particular use of the new cloning technology is certainly not the only one. Cloning technology is simply another piece of this particular puzzle, the genetic engineering of better organisms. Far from being inferior to the originals, clones will likely be better. Every clone begins as a single cell, and must develop and grow in a mother just as every mammalian organism always has.

The technology to create fully developed and mature "clones", identical to the originals, simply doesn't exist, and may not even be possible. That image of cloning is entirely the realm of science fiction. Cloning is a great advance in molecular and cellular biology, and it's many benefits may soon be realized.