<ComboBox HorizontalAlignment="Left" Margin="72,12,0,0" VerticalAlignment="Top" Width="161.333"
	ItemsSource="{Binding Sections}" 
        SelectedItem="{Binding SelectedSection, Mode=TwoWay}"
	IsEnabled="{Binding ElementName=chbSection, Path=IsChecked}">
</ComboBox> 

private void DeleteSection()
{
       MyClass.RemoveSection(SelectedSection);
       SelectedSection = null;
       RaisePropertyChanged("Sections");
}

private readonly List<ISection> _sections;
public IEnumerable<ISection> Sections()
{
    return _sections;
}

public IEnumerable<ISection> Sections()
{
    foreach (ISection section in _sections)
        yield return section;  
}