From http://www.icmag.com/ic/showthread.php?t=31919
Some of the quotes I have read in High Times saying that you get genetic degeneration by keeping mother plants long term, this is total rubbish!
Degeneration can certainly occur if a mother plant gets infected with a reversion virus. I will cover this later! The grass produced today from our mother plants is just as potent and smells just as good as when it was first grown out from seed many years ago. In fact it is better now, we have better lighting and superior growing techniques, allowing the clones to express their potential more fully.
I am going to start by showing you our largest mum, this time from above. She is in a 1-litre pot (the largest size used). With all the top growth pictured she is about 13 inches tall and ready to take cuttings. Inset is a cutting being clipped out see below.