i have got some basic doubts please clear it. .

1) why is it that when you cut by the the same restriction enzyyme , the resultant DNA fragment is have the same kind of "sticky -ends" ??

2) why is it that ulness one cuts the vector and source DNA with the same restriction enzyme, the recombinant vector molecule cannot be created.?

please ANSWER THEM

1. It is because each restriction enzyme recognises specific DNA sequences and cuts each of the two strands of the double helix DNA at specific points in their sugar phosphate backbones. Hence, the resultant DNA segment always have the same kind of sticky end.
2. The vector and source DNA should be treated with the same restriction enzyme so as to produce DNA fragments carrying same (sticky or blunt) ends. These ends are then sealed by the enzyme ligase.