Develop a musical composition by integrating the alphabetically represented musical pattern and the supplied melodic theme.
X:1
L:1/4
M:3/4
K:G
['A G']  
X:1
L:1/4
M:3/4
K:G
 D | D2 F | G2 A | F2 G | A G A | A B A | G F E | D D D | D2 A | G A G | A A G | c B A | B2 D | 
 B2 A | A B G | D E F | G2 |]  