Design a musical composition incorporating the alphabetic expression of the chosen structure and the provided melodic theme.
X:1
L:1/8
M:2/4
K:G
['AB cA', 'AG FD', 'Bc AG']  
X:1
L:1/8
M:2/4
K:G
|:"^Blasket Islands" AB cA | AG FG | AB cA | AF G2 | AB cA | AG FD | DG AB | cA G2 :: AG FD | 
 AG FD | DG AB | cA GF | AG FD | AG FD | DG AB | cA G2 ::"^variation pt.1" B2 Bc | AG FD | B2 Bc | 
 AF G2 | B2 Bc | AG FE | DG AB | cA G2 :|  