Hello everyone,

Sorry, it's such a basic question, but what's the meaning of a 1.5 fold change cutoff for downregulated genes?

For upregulated genes, in my understanding, it means a 50% increase. For example, considering the expression of the same gene in conditions A and B as

A = 100

B = 150

so,

B/A = 1.5

and I would say the gene is upregulated in condition B in relation to condition A, and B represents 150% of A or a 50% increase.

Is that correct? Or may I misunderstanding the meaning of fold change? And what's the equivalent logic for downregulated genes? I would appreciate any recommendation of material explaining these concepts (in the "for dummies" style ;)

Thank you!

This is the way I'm filtering the downregulated genes (logFC < -0.584 or FC < 0.667), but I don't really understand it...

In the example, FC = 0.667 means A represents about 67% of B, that is, a 33% decrease. But the opposite represents a 50% increase.

FC cutoff aims to filter for genes with the same degree of change in both directions (up and down). How FC = 0.667 and FC = 1.5 can be equivalent?

May I interpreting in a wrong way?

They are equivalent in a multiplicative sense as 1.5 x 0.667 = 1. You want to use a multiplicative sense in this case since you're measuring how "many

timesmore" condition A is than condition B.Another way to think of it is that if A is 150% of B, then B is 67% of A, so the equivalent "fold change for downregulated genes" corresponding 150% is therefore 67%.

Maybe I can understand...

I can not explain in a general way, but I can think in terms of physical things like lengths of bars...

If you have a

bar A with length 100and abar B with length 150, then the difference between them is 50 units.You can say both

bar A is 50 units smaller than bar BORbar B is 50 units greater than bar A, but the difference is always the same, it doesn't matter the direction of comparison.You can also say

bar A has a 33% decrease in relation to bar BORbar B has a 33% increase in relation to bar A(as the difference represents 1/3 of 150)??? Then, the degree of change would be the same???Thinking this way, a FC cutoff of 1.5 would represent a 33% increase/decrease...