I have labelled the probes with bacterial artificial chromosome (BAC) DNA ( from RP11 library). 

I used it to do Fluorescence in situ hybridization (FISH), but I don't know how much COT 1 DNA I should put in to suppress the repetitive sequences.

For example, I used 340 ng of probes, cot1 DNA ( invitogen- 1ug/1 ul), so I need to use 34 ul of Cot1 DNA ( if COT1 DNA is 100 fold excess of probes).

Can anyone recommend any other ratio?

Many thanks for your help,

Cheers,

Cuc