Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
Q:1/2=80
M:2/2
K:G
['G/G/G BG', 'AF TA2']  
X:1
L:1/8
Q:1/2=80
M:2/2
K:G
 G/G/G BG AF TA2 | G/G/G BG cABG | G/G/G BG AF TA2 | Bggd B2 G2 :: Ggd=f AF TA2 | Ggde =fgag | 
 =fefc AF TA2 | Gggd TB2 G2 |]  