 A clone is a member of a population of genetically identical cells produced from a single cell.  Cloned colonies of bacteria and other microorganisms are easy to grow, but his not always true for multicellular animals, especially animals.

 Original attempts to clone animals using adult stem cells generally failed.  However, in 1997 Scottish scientist Ian Wilmut stunned the world by announcing he had successfully cloned a sheep.  So how did he go about cloning Dolly?

 1 st – A mammary cell is extracted from a sheep and grown in nutrient- deficient solution that stops the cell cycle in the G1 checkpoint.

 2 nd – A nucleus is removed from an egg cell from another sheep with a micropipette.  3 rd – The mammary cell is inserted inside the covering of the egg shell 4 th – An electric shock causes the cell membranes surrounding the two cells to leak so that the contents of the mammary cell pass into the egg cell. Also, the shock initiates cell division.

 5 th – The embryo begins to develop as the cell continues to divide during mitosis.  6 th – The embryo is implanted into a surrogate mother.  7 th – After five months of pregnancy an identical sheep is born.

 Since dolly scientists have successfully cloned mice, cattle, goats, and pigs.  However, only a small percentage of the transplanted embryos survive to term. Most die late in the pregnancy.  Others become oversized in a condition called large offspring syndrome.  So what’s going wrong?

 Scientists have learned about something called reprogramming. Often time the sperm or the egg is conditioned by switching on and off genes without altering the DNA.  Methyl groups (CH3’s) are added to cytosine units in a gene. The groups turn off the gene and the gene is not expressed.  Other times Methyl groups maybe added to a gene that turns off a gene (like a light switch). So the Gene remains on and can’t be turned off.  This process is known as genomic imprinting.

 Normal development depends on precise genomic imprinting.  Sometimes it takes months or years for proper genomic imprinting to take place in an adults reproductive tissue.  During cloning reprogramming the DNA with genomic imprinting must happen in minutes. Its just not enough time for the process to happen correctly.

 All of the cells in your body form from a single cell, the fertilized egg.  The fertilized egg begins to divide until it eventually forms a blastocyst. The outer layer of the blastocyst forms the placenta.  The inner layers of cells are called embryonic stem cells and can become any type of tissue in the body.

 Because embryonic stem cells can turn into any type of tissue, they offer the exciting possibility of restoring damaged tissues such as muscle or nerve tissue.  Scientists have already been successful at growing heart muscle cells and integrating them into the heart tissue of a living mouse.  So how does it work?

 1 st Fertilized embryos are destroyed. A large percentage of the public believes life begins at fertilization.  2 nd The successful experiments occurred in mice with disabled immune systems. The mice would have probably rejected the new tissue because it would have been seen as a foreign invader. Implant patients often reject new organs for the same reasons.

 1st - Each tissue has tissue-specific stem cells or adult stem cells. Using adult stem cells seems to solve the first problem.  Adult neural stem cells have been used to cure multiple sclerosis in mice.  The injected cells migrated all of the brain and were able to convert themselves to missing cell types and repair disease cells.

 2 nd - Using a similar process used to clone Dolly scientists have created stem cells using the subjects own cells. This is called Therapeutic cloning.  However, problems with this method persists in regard to genomic imprinting discussed earlier.  The process has other more complicated issues as well.