Go in Properties of combobox in event selectionindexchanged write this code
Protected Sub DropDownList1_SelectedIndexChanged(sender As Object, e As System.EventArgs) Handles DropDownList1.SelectedIndexChanged
Dim selectedItem As String
Dim gender As String
selectedItem = DropDownList1.SelectedItem.Text.ToString()
If selectedItem = 'Male' Then
gender='male'
End If
End Sub