library screening

[Melissa Callahan]

Hi,
I'm wondering:  how does one know when they have saturated a screen?  
Specifically, I'm using a degenerate PCR strategy to clone new members of a 
gene subfamily; how do I know when a source of cDNA (excised from Lambda Zap 
II library) is no longer going to yield new clones?  Or:  how do I 
statistically predict when a source of RNA is no longer going to yield new 
clones by RT-PCR?  

Thanks, Christie