Receding Gumline?

I'd never even heard of this until my sister ran into problems several years back. Is it genetic? Is it poor hygiene? Is it just crummy luck? Well, I'd been telling myself that I really needed to make an appt to see the dentist. I guess that this was the kick in the a** I needed!
I was going through my evening routine last night (floss & brush, wash/tone/moisturize) when I noticed a black spot at the bottom of one of my teeth. I'd been keeping an eye on this tooth because the gum has been slowly receding for the last few years. I tried to scrape the black part off, thinking it was perhaps something removable. Alas, I succeeded only in removing a teeny piece of what I assume to be my gum. And I don't have any to spare there! So I had the momentary thought that this was a dental emergency and if I opened my mouth my teeth would all fall out. Fortunately it was only a brief moment of insanity.
I called the dentist's office today and have an appt for tomorrow afternoon. It couldn't come soon enough to suit me! I'm not certain what he will suggest. I know that in my sister's case they removed skin from the roof of her mouth and grafted it onto her gums. They were able to do this in the dentist's office. But it was a different dentist. So we shall see. Say a little prayer. Perhaps to the Tooth Fairy?