Gene/Trait Expression?

[Seratheunicorn]

Hi! I have two questions about basic principles of genetics:

So, first, in cases where a trait is influenced by multiple different genes, is it possible for the trait to be expressed when the person only has some of these gene variants?

Second, if a trait is caused both by genetics and environmental factors, is it possible for someone who doesn't have the gene variant in question to express the trait just from the environmental factors?

Thank you so much!

~Sera