Louie, if the ukulele were tuned in fifths you could not use guitar chord shapes. (You could use
mandolin shapes however, since mandos
are tuned in fifths -- GDAE). I had a friend (now passed away) that used to buy cheapo soprano or concert ukes, then change the string gauges so they could be tuned like a mandolin. He sold a bunch of those as inexpensive travel / practice instruments to mandolin players.
Standard uke tuning lets you use guitar shapes, but the names are three letters higher on ukulele. The guitar "D" shape becomes a "G" chord on ukulele. The guitar "C" shape becomes an "F", but you don't have the pesky bass strings to worry about -- it is a two-finger chord. Put another way, if you capo a guitar at the fifth fret and remove the two bass stings, you essentially end up with a low-G tenor ukulele. Hope this helps.
For baritone DGBE tuning, the chord shapes are just like guitar, but you only have the upper four strings (no bass). Baritone was invented to let guitar players have a ukulele without learning to transpose.
