Develop a musical piece incorporating the designated alphabet-based pattern and the supplied melodic theme.
X:1
L:1/8
M:2/4
K:A
['a>g fe', 'A>c ec']  
X:1
L:1/8
M:2/4
K:A
|: a>g fe | fe e2 | f>e ec | Bc ef/g/ | a>g fe | aA A z | f>g fe | c2 B2 :: A>c ec | ec ec | 
 A>c ec | f>g fe | a>g fe | aA A z | f>g fe |1 c2 B2 :|2 f2 g2 ||  