Create harmonious melodies following the given letter notation and incorporating the designated theme.
X:1
L:1/8
M:2/4
K:G
['ddBB GGD z']  
X:1
L:1/8
M:2/4
K:G
 ddBB | GGD z | ddBB | GGD z | GGAA | BBAA | BGAD | GGGG |]  