There are lots of different types of cloning that biologists use, but the one that most people are familiar with is the idea of creating an identical organism to one that already exists – Dolly the sheep was the first example of this, it was a few years ago now:
Dolly was cloned using a rather technical sounding process called ‘somatic-cell nuclear transfer’, SCNT for short. Basically, you take a cell from the organism you want to clone, and remove the ‘nucleus’ from the cell – this is the bit that contains all of the genetic information and makes the organism unique. You then put this nucleus into an ‘egg’ cell (the same as would be fertilised in normal reproduction) and set the egg cell going to start dividing and growing. Once the cell has divided a few times, the resulting group of cells is implanted into another organism with very similar DNA to that of the clone so it can grow to maturity and be born.
Scientists are looking at using similar techniques with human ‘stem-cells’ – these are cells which aren’t specialised in any one area (like a liver cell for example) that can grow into any type of cell with the right encouragement. These stem cells could be grown into new organs, or injected into someone and used to treat diseases like Parkinson’s by growning new cells to replace damaged ones!