fetching values from sheet1 and putting in drop down list in sheet2

Hi All,

I have 2 sheets: sheet1 and sheet2

in sheet1 the values will be like this:

Type	Description
Alfa	A
Numeric	B
	C
	D
	1
	2
	3
	4

in sheet2 column A will have drop down with Alfa and Numeric values. and in column B based on the selection in column A it should display Alfa or Numeric values in drop down.

like for eg:

if i select Alfa in A1, then in B1 it should show A,B,C,D in drop down list. These values(A,B,C,D or 1,2,3,4) will be fetched from sheet1 and can be changed anytime.

Please help.

Thank you.