Foreign Keys are not Replication

HiWe are using sql server 2005.Replication is Transactional updatable replication.Foreign Keys are not replicating.All parent tables are in replication.When i checked from subscriber only primary and unique key are replicated.I didn't find foreign keys.At Article properties Copy foreign key constraints value is set to False.Can anyone please share some knowledge what will be the impact if we keep the value to False or True.