In [2]:

from itertools import product

list(product(['a', 'b', 'c'], [1, 2]))

[('a', 1), ('a', 2), ('b', 1), ('b', 2), ('c', 1), ('c', 2)]

In [1]:

list(set(product(['nucleus'], [1])).union(product(['embryo'], [1, 2, 4, 5])))

[('nucleus', 5), ('embryo', 1), ('nucleus', 1), ('nucleus', 4), ('nucleus', 2)]