necessary and sufficient conditions - (Mar/11/2008 )

OK so something is necessary if you get rid of it and you don't see the normal wild type effect. And something is sufficient if only that one thing is enough to cause the effect. But how do you find something sufficient in a biological system if you can't get rid of every other thing?

I hope I'm phrasing this correctly...

Thanks for any help!

all seems a bit confusing but i think your definitions are correct

nessesary is a negative effect (lack of = effect)
sufficient is a positive effect (presence = effect)

thus presence + effect = sufficient (other stuff is irrelevant)

dom?
(youre making me doubt myself )

Just an example that's pretty easy to understand:

You find a domain in protein X that you think is responcible for a localization event (ie: amino acids 45-92 in protein X is responcible for the protein's localization to the membrane).

Necessary- if you delete these amino acids from protein X and express it in cells, you see that the expressed protein is not localized to the membrane anymore. These amino acids are necessary for the localization of protein X.

Sufficient- if you tag amino acids 45-92 of protein X with GFP and express it in cells, you see that the expressed GFP protein is localized to membranes. These amino acids (of protein X) are sufficient to localize GFP to membranes.