Dominant traits are passed on to a child from at least one affected parent. This results in a trait that does not skip generations. Recessive traits can be masked by dominant genes. This means that both parents can be carriers and have an affected child, resulting in a recessive trait that can skip generations.
Pedigrees show the presence or absence of a trait through several generations of a family by using a series of symbols to represent family relationships, with squares representing males and circles representing females. A marriage is shown by connecting two symbols with a horizontal line. When children result from a union a vertical line drops down from the couple, and the children are represented below the couple. This results in an diagram with successive generations occurring in a vertical pattern, with the oldest generation at the top of the pedigree and the youngest generation at the bottom. The presence of a trait is indicated by a shaded circle or square, while the absence of a trait is indicated by a clear symbol.
