Dropdown list cell populated automatically

Hi
I have several drop down lists in a row, at the end of the row I press TAB and a new row is created. I want one of the the dropdown boxes that is created in the new row to not be blank and to populate the cell its in with one of its list.

Difficult to explain but when a new row is created all cells are blank, I want one of the dropdown boxes that has "Yes" and "No" in its list to populate the cell with "No" automatically, I will change it to Yes when needed.

Not sure this is possible but can anyone help

Many Thanks

Processchip