Better more fun video on cleaning sensor.Welcome to Interchangeable Lens Cameras (ILCs). Any camera with a changeable lens will be prone to dust on the sensor. Cleaning them is easy, so don't sweat it too much, just get the right cleaning tools and learn how to do it and you're set.
For a Sony E-mount with 4K the new a7rII is awesome! But carries a hefty price tag: