A pedigree is a diagram that maps how a trait or health condition passes through generations of a family. In genetics, it’s the primary tool used to visualize inheritance, showing who in a family carries, expresses, or is unaffected by a particular trait. Outside of genetics, the term also refers to the documented ancestry of purebred animals. Both uses share the same core idea: tracking lineage to understand what gets passed down.
How a Pedigree Chart Works
A genetic pedigree looks like a family tree, but instead of just showing names and relationships, it uses standardized symbols to convey biological information at a glance. Squares represent males, circles represent females, and filled-in (shaded) shapes indicate individuals who express the trait or condition being studied. A diagonal line through a symbol means that person is deceased.
Lines connect the symbols in specific ways. A horizontal line between a square and circle shows a mating pair. A vertical line dropping down from that pair is called a line of descent, leading to their children. Siblings are connected by a horizontal sibship line. Each row of the chart represents one generation, so you can trace a trait from grandparents to parents to children simply by reading from top to bottom.
These symbols were standardized by the National Society of Genetic Counselors, and the core notation published in 2008 remains the current professional standard, with recent updates focused on how sex and gender are represented.
What Pedigrees Reveal About Inheritance
The real power of a pedigree is pattern recognition. By looking at which family members are affected and which are not, you can often determine how a trait is inherited. There are several major inheritance patterns, and each leaves a distinct visual signature on the chart.
Autosomal Dominant
A trait is likely autosomal dominant when every affected child has at least one affected parent. The trait doesn’t skip generations because you only need one copy of the gene variant to show it. It appears equally in males and females, and an affected father can pass it to his sons, which rules out X-linked patterns.
Autosomal Recessive
The hallmark of autosomal recessive inheritance is that affected individuals can have two completely unaffected parents. Both parents carry one copy of the gene variant without showing symptoms, and a child who inherits a copy from each parent expresses the trait. This pattern often appears to “skip” generations, with affected individuals showing up seemingly out of nowhere in families where no one else looks affected.
X-Linked Recessive
X-linked recessive traits are far more common in males than females. Because males have only one X chromosome, a single copy of the variant is enough to produce the trait. The defining rule: there is no father-to-son transmission, since fathers pass their Y chromosome (not their X) to sons. If a mother carries the trait on one of her X chromosomes, each of her sons has a 50 percent chance of being affected. If a mother actually expresses the trait herself, all of her sons will have it.
Mitochondrial
Mitochondrial DNA is inherited exclusively from the mother. That means a mitochondrial trait follows a strict maternal line: an affected mother passes it to all of her children, but an affected father passes it to none. On a pedigree, this creates a distinctive pattern where the trait flows only through female lineage, though both sons and daughters can be affected.
How Pedigrees Are Used in Genetic Counseling
When you visit a genetic counselor, one of the first things they do is build a pedigree. They’ll ask about your family’s medical history, record which relatives have had certain conditions, note ages of onset, and chart relationships across multiple generations. This becomes the foundation for assessing your risk of carrying or passing on a genetic condition.
The counselor uses the completed pedigree to identify which inheritance pattern best fits the family’s history, then calculates the probability that future children or other family members could be affected. For example, if a pedigree suggests autosomal recessive inheritance and both parents are identified as carriers, each pregnancy carries a 25 percent chance of producing an affected child. This kind of concrete risk assessment helps families make informed decisions about genetic testing, family planning, or monitoring.
Why Pedigrees Can Be Tricky to Interpret
Real families don’t always produce textbook-clean pedigrees. Several biological factors can muddy the picture. Incomplete penetrance means a person can carry a disease-causing gene variant and never develop symptoms. This can make a dominant condition look like it skipped a generation, mimicking a recessive pattern. Variable expressivity adds another layer: family members with the same genetic variant may show very different severity of symptoms, from barely noticeable to severe.
These complications explain why apparently unaffected parents sometimes pass pathogenic variants to affected children, and why some people’s genomes contain potentially damaging variants without any obvious health effects. For clinicians, this can lead to delayed or incorrect diagnoses, which is why pedigree analysis is typically one piece of a larger diagnostic process that includes genetic testing.
Small family size also limits what a pedigree can tell you. Inheritance patterns become statistically clearer with more individuals across more generations. A family with only one or two children per generation may not produce enough data points to confidently distinguish between dominant and recessive inheritance.
Pedigrees in Animal Breeding
Outside of human genetics, “pedigree” most commonly refers to the documented lineage of a purebred animal. Under U.S. federal regulations, a purebred animal must be the offspring of known, registered ancestors of the same recognized breed, with at least three generations of traceable ancestry.
A pedigree certificate is an official document issued by a breed registry association. It records the animal’s ancestry, color and markings, the breeder’s name and address, and every subsequent owner. For animals imported into the United States, the pedigree certificate must include a complete chain of ownership from breeder to importer, with descriptions of markings translated into English. These documents serve as proof of breed purity and are required for registration, breeding programs, and international trade in purebred livestock.
The logic is the same as in genetics: by tracking who descended from whom, breeders can predict which traits offspring are likely to inherit and make informed decisions about which animals to pair.