Bloodline: All of the vampires descended, through Deliberate Transformation, from a specific Spontaneous Transformation.

“You’ve noticed that the vampires here all have slightly different abilities?”

I shook my head. “Except Mircalla. She can do some freaky shit.”

“Yes, well. Vampirism didn’t spring up from one isolated source. We all evolved slightly differently in different places, and there are different abilities and characteristics associated with each of these Lines.”

-Josephine and Grant – Black, Chapter 12

Each vampire created through Spontaneous Transformation has a unique set of traits that are handed down through the generations. It works much like genetic traits, only there is no second parent to offer other traits; which leaves the variations in offspring annoyingly unexplained.

Vampires are like snowflakes, each one is different. Vampires of the same bloodline are more likely to share line-specific traits with each other than they are to share them with those of a different bloodline, but it’s not guaranteed. And the strengths of specific powers between related vampires can vary greatly too.

At this point there are only two specific lines that I know about: the Gypsies and the Judeans. The Line of the Dragon is mentioned in Black, but not discussed. Although there are certainly more lines that have yet to make their way into Catherine’s stories.