Vertical scrollbar not found in datagrid inside usercontrol in wpf

I have a user control in WPF with a DataGrid. I am adding this user control to the window inside the TabItem TabControl. The vertical scrollbar does not become visible. I resized the window and it seems like the user control is at full height after considering the height of the DataGrid.

How to create a vertical scroll bar and keep the height of the DataGrid in automatic mode depending on the height available by the height of the user control and window?

EDIT: Main window:

<Window>
  <Grid>
    <TabControl Name="tc"
                SelectionChanged="tc_SelectionChanged">
      <TabItem Header="ABC">
        <local:uc1 />
      </TabItem>
      <TabItem Header="DEF">
        <local:uc2 />
      </TabItem>
    </TabControl>
  </Grid>
</Window>

User control:

<UserControl>
  <Grid>
    <Grid.RowDefinitions>
      <RowDefinition Height="Auto"></RowDefinition>
      <RowDefinition Height="30"></RowDefinition>
    </Grid.RowDefinitions>
    <Grid.ColumnDefinitions>
      <ColumnDefinition Width="2*"></ColumnDefinition>
      <ColumnDefinition Width="*"></ColumnDefinition>
    </Grid.ColumnDefinitions>

    <StackPanel Grid.Row="0"
                Grid.Column="0"
                Orientation="Vertical">
      <StackPanel Orientation="Horizontal">
        <Button>Add</Button>
        <Button>Remove</Button>
        <Button>Refresh</Button>
      </StackPanel>

      <Label Name="lblTopMessage">some message</Label>

      <DataGrid Name="dg"
                IsReadOnly="True">
        <DataGrid.Columns>
          <DataGridTextColumn Binding="{Binding Name}"
                              Header="Name"
                              Width="*"></DataGridTextColumn>
          <DataGridTextColumn Binding="{Binding Value}"
                              Header="Value"
                              Width="130"></DataGridTextColumn>
          <DataGridTextColumn Binding="{Binding List}"
                              Header="List"
                              Width="*"></DataGridTextColumn>
        </DataGrid.Columns>
      </DataGrid>

    </StackPanel>
    <Grid Grid.Row="0"
          Grid.Column="1"
          Name="gridTS">
      <Grid.RowDefinitions>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
        <RowDefinition Height="Auto"></RowDefinition>
      </Grid.RowDefinitions>
      <Grid.ColumnDefinitions>
        <ColumnDefinition Width="100"></ColumnDefinition>
        <ColumnDefinition Width="*"></ColumnDefinition>
      </Grid.ColumnDefinitions>
      <TextBlock Name="lblNewSource"
                 Grid.Row="0"
                 Grid.ColumnSpan="2"
                 HorizontalAlignment="Center"
                 Padding="0 5 0 0"
                 FontWeight="Bold">New Source</TextBlock>
      <TextBlock Grid.Row="1"
                 Grid.Column="0"
                 Padding="10 10 0 0">Name:</TextBlock>
      <TextBlock Grid.Row="2"
                 Grid.Column="0"
                 Padding="10 10 0 0">Value:</TextBlock>
      <TextBlock Grid.Row="3"
                 Grid.Column="0"
                 Padding="10 10 0 0">List:</TextBlock>

      <TextBox Grid.Row="1"
               Grid.Column="1"
               Name="txtName"
               IsEnabled="False"></TextBox>
      <ComboBox Grid.Row="2"
                Grid.Column="1"
                Name="cbValue"></ComboBox>
      <ListBox Grid.Row="3"
               Grid.Column="1"
               Name="lbList">
        <ListBox.ItemTemplate>
          <DataTemplate>
            <CheckBox Margin="3 5 0 3"
                      Content="{Binding Name}"
                      IsChecked="{Binding IsActive}" />
          </DataTemplate>
        </ListBox.ItemTemplate>
      </ListBox>

      <Button Name="btnSave"
              Click="btnSave_Click"
              Grid.Row="4"
              Grid.Column="1">Save</Button>
      <TextBlock TextWrapping="WrapWithOverflow"
                 Name="lblMessage"
                 Grid.Row="5"
                 Grid.Column="1"
                 Margin="0 10 10 0"></TextBlock>
    </Grid>
  </Grid>
</UserControl>