A pedigree is a diagram that maps biological relationships across generations of a family, showing who is related to whom and which individuals carry or are affected by a particular trait or disease. In genetics and medicine, it’s the primary tool used to trace how conditions pass from parents to children. In animal breeding, it serves as a certified record of an animal’s ancestry. The word itself comes from the French “pied de grue,” meaning crane’s foot, because the branching lines in early family diagrams resembled the toes of a crane.
How a Pedigree Chart Works
A pedigree uses simple geometric shapes arranged in rows, with each row representing one generation. Squares represent males, circles represent females, and a horizontal line connecting a square and circle indicates a mating pair or partnership. Children are drawn below their parents, connected by vertical lines dropping down from the horizontal partnership line. Siblings share a common horizontal line above them.
Individuals affected by the trait or condition being studied are shown with filled-in (shaded) shapes, while unaffected individuals remain open. A diagonal line drawn through any symbol indicates that person is deceased. If biological parents are separated or divorced, a slash is drawn through the horizontal line connecting them. When a parent has children with a different partner, a second relationship line extends to that partner. To save space, a number can be written inside a symbol to represent multiple siblings of the same sex, so three unaffected brothers might appear as a single square with the number three inside.
A standard medical pedigree covers at least three generations. This depth gives enough information to spot patterns that point toward a genetic cause. Collecting the information can be as simple as asking a patient whether relatives share the same illness, or as detailed as documenting medical and psychosocial relationships for every family member.
Symbols for Special Situations
Pedigrees need to capture the full complexity of real families, so the symbol set goes well beyond basic squares and circles. A diamond shape is used when a person’s sex is unknown. Pregnancy losses, including miscarriage, stillbirth, or elective termination, have their own designated symbols. When two partners are biologically related to each other (a consanguineous relationship), the horizontal line connecting them is doubled. If the exact degree of relatedness isn’t obvious from the chart itself, the specific relationship (such as “second cousins”) is written above that double line. Consanguinity matters because related parents are more likely to both carry the same recessive gene variants, increasing the chance their children will be affected.
Spotting Inheritance Patterns
The main reason to draw a pedigree is to figure out how a trait is inherited. Different inheritance patterns leave distinct fingerprints across generations.
Autosomal Dominant Traits
When a condition is autosomal dominant, only one copy of the altered gene is needed to cause it. Every affected person has at least one affected parent, and the trait tends to appear in every generation, creating what geneticists call a vertical pattern running from the top of the pedigree to the bottom. Because these conditions are usually rare, most affected individuals carry just one copy of the variant rather than two. It is possible, though, for an affected parent who carries one copy to have entirely unaffected children, depending on which gene copy each child inherits.
Autosomal Recessive Traits
Recessive conditions require two copies of the altered gene, one from each parent. The hallmark on a pedigree is that affected individuals can appear even when neither parent shows the condition, because both parents can silently carry a single copy without symptoms. This often makes the trait look like it “skips” generations. Fewer family members are affected overall compared to a dominant pattern, and unaffected individuals can have affected children, which is the clearest clue that the inheritance is recessive rather than dominant.
Pedigrees in Medicine
In clinical genetics, a three-generation pedigree is considered the most efficient way to assess whether a disease has a hereditary component. When a lab analyzes a patient’s DNA and finds a variant of uncertain significance, the family pedigree provides crucial context. A variant is more likely to be classified as disease-causing if the patient’s family history fits a recognizable pattern for a single-gene disorder. For example, if a patient has a new (de novo) variant and both parents are unaffected, that pattern strengthens the case that the variant is responsible for a dominant condition.
Digital tools have largely replaced hand-drawn charts in clinical settings. Modern pedigree software can generate diagrams automatically from structured patient data, link each family member’s conditions to standardized medical vocabularies, and update in real time as new information comes in. This means a clinician can enter family data step by step without needing to plan the layout, and the software handles the drawing. Because the underlying data is structured rather than stored as a static image, it can be shared between medical information systems and reused for future analysis.
Pedigrees in Animal Breeding
Outside of human genetics, pedigrees are most familiar in the context of purebred animals. An AKC certified pedigree for a dog, for instance, lists the registered names and registration numbers of ancestors across multiple generations, along with coat colors, markings, breeder and kennel names, and any titles earned in show championships, field trials, obedience competitions, or hunting tests. Health screening results, such as orthopedic or eye certification numbers, may also appear.
Breeders use pedigrees to calculate a coefficient of inbreeding, which estimates what percentage of an animal’s gene pairs became identical because its parents shared a common ancestor. An animal with a coefficient of 12.5%, for example, is expected to have 12.5% more identical gene pairs than the population average. Higher coefficients raise the risk of inherited health problems. The key principle is straightforward: an individual is inbred if and only if its parents are related through one or more common ancestors. Inbreeding can be reduced to zero in a single generation simply by pairing unrelated animals, which is why pedigree records are so valuable for planning matings that maintain genetic diversity.
Why Pedigrees Still Matter
Despite advances in direct DNA testing, pedigrees remain essential because they provide something a genetic test alone cannot: context. A single gene variant means little without knowing whether it tracks with disease across a family. A pedigree reveals whether a condition follows a dominant, recessive, or sex-linked pattern, whether it appeared spontaneously or was inherited, and which family members might be at risk even if they show no symptoms. For animal breeders, it guides decisions that shape the health of future litters or herds. Whether sketched on paper or generated by software, the pedigree is still the foundation of genetic reasoning.