I have used the technique and found it useful. How do you know you have resp deficient yeasts? I see two colonies that appear to be petite - how have these been confirmed as resp def?. assiume you used the medium s desribed- without polysorbate or similar addition.

Phil Geis It isn't confirmed that the yeasts are respiratory-deficient, I am trying to use the method to identify these colonies after they are afffected by EthBr. I used YPD medium.

Sure don't see many petite colonies What was your mutagenesis protocol.

Phil Geis It was based on this article: Article Petite Mutation in Yeast

"Induction of petites with ethidium bromide: EthBr (10 ug/ml.) was added to logarithmically growing cells in yeast nitrogen base-glucose."

You're wotking with Saccharomyces cerevisiae?

Phil Geis yes

The colonies appear to be of about the same size in both ifugre. Doesn;t seem that petites were generated.

Phil Geis but what about the color? Is it okay that all the colonies turned red?

Would have expected a deeper red with TTC and resp competent. But it's been too long since the experiment to recall what I saw with the yeast.

Phil Geis thank you for your answers