How to create dependent dynamic dropdownlist?

How can I create a dependent dynamic dropdownlist in php. All of the dropdownlist contents / data's will come from the database (I have no problem populating the d开发者_JAVA技巧ropdownlist with the database content)

i.e

dropdownlist 1

dropdownlist 2

If I select "fruits" on the dropdownlist 1 it will display items on dropdownlist 2 such apple, orange, grape.

Second question:

Is there any counter part of the asp.net updatepanel here in php?

Thanks.

Dynamic Drop Down List for PHP