If the sequence of bases on one 'sticky end' formed by the action of EcoRI is AATT on a Vector DNA, the sequence of bases on 'sticky end' of foreign DNA to which these can join, would be:

TTAA

The correct answer is Option (2) - TTAA

Explanation:

• EcoRI is a restriction enzyme that cuts DNA at the palindromic sequence 5'-GAATTC-3', producing sticky ends with the overhang sequence 5'-AATT-3' on one strand.
• The complementary sticky end must pair with this overhang via base pairing rules (A pairs with T, T pairs with A).
• Therefore, if the vector has a 5'-AATT-3' overhang, the foreign DNA must have the complementary 3'-TTAA-5' overhang to ligate properly.

Other options:

TATA → Incorrect, does not pair with AATT.

TTAA → Correct, as it is complementary to AATT.

AATT → Same as the vector’s sticky end, not complementary.

UUAA → RNA sequence (Uracil is not present in DNA).