The pedigree method consists of an analysis for a particular trait, when the results have already been made. Usually diagrams or charts are used to attempt to find patterns of inheritance. Pedigrees are the oldest methods of genetic information and are still used in studies of human inheritance and animal breeding. The first step is to determine whether the gene being studied is dominant or recessive. Recessive genes are difficult to keep track of, for they are hidden by their dominant alleles one generation after another. An important thing to remember is that one can not determine offhand which individual is a carrier of a specific trait, until the trait is expressed in someone.

Traits that are dependent on certain recessive genes may suddenly appear without any previous record of a relative having this trait. Recessives are more likely to become expressed in families where the father and mother are closely related, or descended from a common ancestor. Next one must identify the genotypes of as many family members as possible with the information given. For example if a man expresses the recessive gene for the trait of adherent earlobes, the man must be homozygous (aa) for his genotype. Both of his parents must be heterozygous (Aa) carriers for each to have contributed a gene to their son. One may then conclude that his brothers and sisters must have the genotype of AA or Aa, but not aa for they do not express the trait of adherent earlobes. The best probability is that each parent is Aa, therefore the likelihood of a child having free earlobes with a genotype of Aa is two-thirds and a genotype of AA, one-third. Without any more information one can assume that the man's sibling's can be Aa with two-thirds probability and a fifty percent chance for being a carrier of the recessive gene, if their parents are also carriers.

Family Pedigree

Pedigree Diagram

Pedigrees are very similar to family trees, except pedigrees study a certain trait within a family. Every generation is represented by a Roman numeral, and each member of the generation by an Arabic numeral. Males are represented by a square and females by a circle. If the symbol is shaded that person expresses or has the studied trait. For example, the two generation pedigree below shows that the father expresses the trait, as does his daughter, but no other family members

Making your own family pedigree is easy. All the materials you will need is paper, a pencil or pen and a colored marker. Draw an outline of your family starting with your grandparents, leading to your parents, uncles, aunts and then yourself, any siblings or cousins. The ability to roll one's tongue is a noticeable dominant trait. Anyone who can roll their tongue has the dominant allele R while those who cannot have the genotype rr. Find out if you can roll your own tongue, if not enter your genotype on the pedigree as rr. If you can, write your genotype as one R for you have the dominant gene. Ask family members on your pedigree if they are able to roll their tongues. Then write down the appropriate genotypes by their symbol on the chart.