As we cannot observe genes directly, we usually study it from their effects.
We call character an observable discrete characteristic we are studying. For example, the lenght of the nose, the colour of the eyes.
Each of the different manifestations of a character, receives the name of phenotype. For example, blue-eyed phenotype, low-levels of insuline phenotype.
To represent the genetic data, we have to draw the genetic relationships between the different individuals, and which is their phenotype. We call these drawings pedigrees, and they are constructed as explained in the video.