Question

how did mendels experiments show that traits may be dominant or recessive

Answer 1

In the F1 generation
Mendel crossed pure tall ( TT ) with pure small ( tt ) , he got all tall plants ( Tt ) .
When he self crossed ( Tt ) then he got both types of plants , small and tall .
This shows that the small character was present in the F1 generation but due to the presence of tall character it wasn't inherited . So tall character is dominant and small character is recessive.