A pedigree chart is a diagram that shows the occurrence and appearance or phenotypes of a particular gene or organism and its ancestors from one generation to the next. Pedigrees use a standardized set of symbols, squares represent males and circles represent females. If the sex of the person is unknown a diamond is used. Someone with the phenotype in question is represented by a filled-in (darker) symbol. Heterozygotes, when identifiable, are indicated by a shade dot inside a symbol or a half-filled symbol.