Cloning works because it isn't only the reproductive cells that can reproduce.
Every living cell of the body contains the genetic blueprints needed to create an entire individual.Scientists take genetic material from a donor cell and insert it in an unfertilized egg from which all the original genetic coding was removed. Equipped with a new blueprint, the egg is tricked into thinking it is newly fertilized.
It divides, grows, forms an embryo. Then, using technology that has been established for many years, the embryo is implanted into a surrogate mother. When the "mother" comes to term, she delivers an offspring that is the carbon copy of the donor.
Donor cells can come from various parts of the body.
Dolly the sheep - whose "Baaa" was heard around the world when Scottish researchers announced the first mammalian cloning in 1997 - was created with genetic material taken from cells in the udder of an adult sheep.
A group in Hawaii copied generations of mice using cumulous cells from the lining of the ovaries. Japanese scientists cloned twin calves from genes in dermal fibroblast cells (cells in connective tissue that form fiber) that they took from the cow's ear.
"No one knows at this stage of the game whether there's a limitation," said USU researcher Kenneth L. White, "whether there are certain types of adult cells that are easier to reprogram than others. It's not even clear that fetal cells are easier to reprogram than adult cells."
White's team has been working for several years to improve cloning. They are focusing on two areas, reprogramming the donor nucleus and "turning on" the newly implanted egg so that it will start to grow.
To extract genetic material from a donor cell and to remove the original genetic plan out of the unfertilized egg, they peer into microscopes working at 200 power magnification and use micro-tools like those used by neurosurgeons.
"These eggs are approximately 150 microns in diameter (75 billionths of an inch), so they're very small. You can't see them with the naked eye," White said.
Think that's small? The genetic material extracted from the donor is only 8 to 10 microns across.
"We can remove the genetic material from the egg, then pick up one of these 10-micron-diameter cells and put it in the enucleated (nucleus removed) egg."
Then the egg divides, the embryo grows and is implanted in a surrogate mom and nature takes its course.