Re: The difference between the cloning of the Rhesus monkey and Dolly?

Dolly was cloned using nuclear transfer, the nucleus was taken out of an 
adult cell and transfered into an unfertilized egg which then developed 
into an embryo.  This resulted in a new animal genetically identical to 
the original adult who donated the nucleus. The rhesus monkey, named 
Tetra, was created by splitting a very early embryo into four pieces.  
This is the same process that can lead to the development of identical 
twins.  Technically this is not cloning since it does not produce the 
genetic duplicate of an adult.

What the investigators did was to create embryos by in vitro 
fertilization.  When the embryos reached the 8 cell stage they were split 
into four parts, each containing two cells.  These continued to divide and 
evenually were implanted into the uteri of different mothers.  All of the 
infants produced from one split egg would be genetically identical.  In 
this case only Tetra survived to birth.

Splitting embryos like this has been done in mice for many years but this 
is the first report in primates.  It is not easy to do however.  So far 
the investigators have made 368 embryos from splitting 107 original 
embryos.  They got 4 pregnancies in 13 tries and only Tetra has survived 
to birth.  

This study was published in the January 14, 2000 edition of SCIENCE 
magazine.