Transitive trust exists when all domain controllers share the same root. Or when you choose to add your domain controller to be part of the existing forest (when you first set up AD)
Now the questions.
Say I have a domain called "dissolved.com" with users Bob, Sally and Tom
I have a child called "software.dissolved.com" with users Ryan, Matt and Dan
1. Do changes replicate in between the 2 domains? Or are they considered seperate?
2. Can Ryan , from the software.dissolved.com domain, log into the dissolved.com domain?
3. Can Bob , from the dissolved.com domain, log into the software.dissolved.com domain?