Re: What are different ways to clone animals and plants??

First, let's define cloning....in this context, it means to produce an 
offspring that is genetically identical to its parent. Why is this hard to 
do? Well... 

During the earliest stages of life, when an embryo consists of fewer
than a dozen or so cells, the genes inside every nucleus have their
fullest potential. Each embryonic cell is totipotent: It has the ability to 
differentiate or develop into any of the possible cell types in the body. As 
an embryo develops, cells lose this ability. 

In a procedure called embryo splitting, which has been available to animal 
breeders for decades, scientists take a young embryo, still composed of 
totipotent cells, and divide it in half or quarters. Each of these portions 
can give rise to a normal animal, so the procedure creates
twins, triplets, or quadruplets.

Replacing the nucleus of an unfertilized egg with the nucleus from another 
cell is what most scientists refer to as nuclear cloning.The feat is 
typically performed by removing the egg's nucleus with a fine, hollow 
needle. A donor cell is fused to the egg by pulses of electricity, which 
break down the donor cell's outer membrane and allow the egg to envelope its 
new nucleus.

The nucleus that created Dolly was 6 years old. 
Moreover, Dolly was the only survivor of 277 cloning attempts with
adult sheep cells. One explanation for the group's low success rate
may be the electric pulses that trick the egg into developing These pulses 
don't always trigger the same signals inside an egg that a sperm's arrival 
does.

In one sense, Dolly isn't even a true clone -- she does not share all
of her genes with her donor. As many scientists have pointed out, a
few dozen genes reside in the energy-producing organelles called
mitochondria. Since only the nucleus of an adult ewe cell was
transferred to the egg, Dolly's mitochondrial DNA comes from the
recipient egg.

This problem of totipotency is not really a problem with plants since most 
plants have meristematic tissues that divide asexually and are able to 
differentiate into diffrent plant tissues. Scientists can transform (or 
introduce unique genes into a plant species) protoplasts (meristematic cells 
whose cell wall has been removed) and then culture these protoplasts into 
true plants.