C# WPF DataGrid.ItemsSource generates new Columns

I use a DataTable as source for my DataGrid:

  dt.Columns.Add("Update?", typeof(Boolean));
  dt.Columns.Add("Emulator", typeof(String));
  dt.Columns.Add("Path", typeof(String));

  ...      

  dataGrid1.ItemsSource = dt.DefaultView;

The XAML code to the DataGrid:

     <DataGrid  AutoGenerateColumns="True" Height="133" HorizontalAlignment="Left" Margin="0,81,0,0" Name="dataGrid1" VerticalAlignment="Top" Width="688"  >
        <DataGrid.Columns>
            <DataGridCheckBoxColumn CanUserResize="False" Header="Update?" />
            <DataGridTextColumn CanUserResize="False" Header="Emulator" IsReadOnly="False"/>
            <DataGridTextColumn CanUserResize="False" Header="Path" IsReadOnly="False"/>
        </DataGrid.Columns>
    </DataGrid>

So if the DataTable is empty I got an empty DataGrid showing the three headers names.
If the DataTable contains items the DataGrid gets extra columns instead of filling the already existing ones.

What can I do that the DataGrid fills up its existing columns?