I have setup POC environment which include ONLY one windows 2008 R2 domain controller, one windows 2008 R2 member server and one windows 7 Pro in vmware workstation for testing.  Could I take snapshot for the domain controller during testing if only one domain controller exists in domain environment?

Are there any side effects for the domain controller if I take snapshot?

As far as I know, we can't take the snapshot on any domain controllers when there are at least two domain controllers in domain environment.

Thank you for your kind assistance.

You can but this is not a supported way to restore. My recommendation would be to have a second disk and use Windows Server Backup feature to backup your DC. However, you can still use the snapshot as it is a PoC environment.

Are there any side effects for the domain controller if I take snapshot?

Technically Yes. You may break the secure channel between your domain controllers and computers. 

Thanks for your valuable comments!!

Thanks for your valuable comments