Pedigree chart: symbols, generations, and how to draw one
A pedigree chart is the standardised diagram that records a family's biological structure and disease history. This page explains what a pedigree chart is, the symbols defined by the National Society of Genetic Counselors (NSGC) and updated in 2022, the three-generation convention, the inheritance patterns visible in a pedigree, and how pedigree charts are drawn today using software rather than paper.
Short version. A pedigree chart is a family diagram drawn with a defined symbol set so that anyone trained on the standard can read it the same way. Squares are males, circles are females, diamonds are unknown or unspecified sex; filled means affected, a diagonal line means deceased, an arrow marks the proband. The current reference is the 2022 NSGC update; the minimum useful family-history record is three generations.
What a pedigree chart is
A pedigree chart is a structured diagram of a family's biological relationships, drawn using a notation set agreed by the genetics community. Each individual is represented by a shape encoding sex assigned at birth; the shape's fill encodes affected status for the catalogued condition; lines connect partners, descend to offspring, and connect siblings into a sibship; an arrow marks the proband — the individual through whom the family came to attention. A pedigree chart is dense: in one diagram it captures who is related to whom, who is affected, who has died, who is a carrier, and the structure that lets a reader follow a possible inheritance pattern across generations.
The same word — "pedigree" — appears in animal breeding, in genealogy, and in human genetics. The notation differs between domains. This page is about the human-genetics pedigree chart, which uses NSGC-standard symbols and is the basis for clinical, research, and educational documentation of family-history information.
The symbol set, in plain language
The current symbol reference is the 2022 update to the NSGC Pedigree Standardization Work Group recommendations, which build on the original Bennett 1995 paper and the 2008 update. The conventions that matter most in routine pedigree drawing:
- Square: male.
- Circle: female.
- Diamond: unknown or unspecified sex.
- Filled / shaded shape: affected for the catalogued condition. Quadrant fills (top-left, top-right, bottom-left, bottom-right) distinguish multiple conditions on the same individual.
- Diagonal line through a shape: deceased. Cause and age at death are annotated below the shape.
- Arrow: proband (the individual through whom the family came to attention).
- Horizontal line between two shapes: partner / mating connection.
- Double horizontal line: consanguineous union.
- Vertical line descending from a partner line: parental descent to a sibship.
- Horizontal line connecting siblings: sibship; siblings are placed in birth order from left to right.
- Triangle: pregnancy, miscarriage, or termination, with gestational age annotated.
- Central dot or half-fill: carrier status (the convention chosen depends on the family / publication).
- Brackets around a shape: adopted individual.
- Roman numerals along the left margin: generation (I, II, III, IV).
- Arabic numerals within a generation: individual identifier (II-3 for the third individual in the second generation).
For the full reference and the detail of the 2022 update on sex versus gender, see NSGC pedigree notation and pedigree symbols reference.
Generations
A pedigree chart is laid out in generations. Each generation occupies a horizontal row, with the oldest generation at the top. Roman numerals down the left margin number the generations: I (great-grandparents or grandparents), II (parents and their siblings), III (proband and siblings, cousins), IV (children of the proband, where applicable). Within a generation, individuals are numbered with Arabic numerals (1, 2, 3...) so that any person can be referred to by an unambiguous identifier such as III-2.
The minimum useful record for family-history documentation is three generations from the proband. Three generations is the threshold at which a pattern across affected and unaffected individuals starts to be informative; with two generations, almost any pattern can be incidental. Four generations is preferred where information is available, and pedigrees that span five or six generations are not unusual in research contexts.
Inheritance patterns visible in a pedigree
The pattern of affected and unaffected individuals across generations and sexes is what makes a pedigree chart informative. The classic patterns:
- Autosomal dominant: affected in every generation, both sexes affected, vertical transmission, ~50% of offspring of an affected parent are affected.
- Autosomal recessive: affected individuals typically appear in a single generation (sibship), unaffected parents who are obligate carriers, both sexes affected, often associated with consanguinity.
- X-linked dominant: affected in every generation, affected males pass the trait to all daughters but no sons, affected females pass to ~50% of children regardless of sex.
- X-linked recessive: predominantly affected males, affected males inherit from carrier mothers, no male-to-male transmission, daughters of affected males are obligate carriers.
- Y-linked: exclusively male transmission, all sons of an affected father are affected, no female transmission.
- Mitochondrial: maternal transmission, affected mothers transmit to all offspring, no paternal transmission.
Real pedigrees rarely fit a single pattern cleanly. Reduced penetrance, variable expressivity, de novo variants, germline mosaicism, X-inactivation, imprinting, and sex-differential severity all complicate the picture. Pattern recognition from a pedigree is suggestive; confirmation requires molecular testing and / or formal segregation analysis. Specific patterns are covered in detail in our pedigree chart examples page.
How a pedigree chart is drawn today
Hand-drawn pedigrees on paper or whiteboard remain part of teaching and bedside use. For documentation, research, and exchange, software is the standard medium. Pedigree-drawing software enforces NSGC notation by default, lays out the family automatically as it grows, exports the result as PDF / PNG / SVG for the printable artefact, and exports the structured data as GEDCOM, PED, Phenopackets, or CanRisk for downstream consumption. The advantage over generic diagram software is enforcement of the symbol set and the structural relationships; the advantage over hand-drawing is consistency and exchange.
Evagene's pedigree drawing tool runs in the browser and draws via a gesture-based interface that is designed to keep up with the conversational pace of family-history collection. The output is NSGC-compliant by default. The structured pedigree can be exported in GEDCOM 5.5.1 for genealogy interchange, PED for linkage workflows, Phenopackets v2 for phenotype-aware exchange, or CanRisk 2.0 for upload at canrisk.org when BOADICEA computation is wanted. PDF / PNG / SVG export covers the printable artefact for slides, teaching, or research notes.
Pedigree chart in teaching
Pedigree charts are core to introductory genetics teaching: students learn the symbol set, work through inheritance-pattern examples, and interpret published pedigrees from research papers. Pen-and-paper exercises remain valuable at the introduction stage; software exercises take over once the symbol set is internalised. Our pedigree charts for biology class page collects worked examples by inheritance pattern, and our pedigree chart template page covers printable templates and when a paper template is appropriate.
Pedigree chart for clinical genetics
In clinical genetics, the pedigree chart is the primary documentation artefact for family-history information collected during a consultation. Genetic counsellors and clinical geneticists draw a pedigree during the consultation, refine it across follow-up visits, and use it as the input to family-history risk-model algorithms (BRCAPRO, MMRpro, PancPRO, Tyrer-Cuzick, BOADICEA via CanRisk). Detail on the clinical-genetics view is in clinical pedigree drawing and clinical genetics pedigree tool.
Frequently asked questions
What is a pedigree chart?
A standardised diagram of a family's biological structure and disease history, using NSGC-defined symbols.
What do the symbols on a pedigree chart mean?
Squares = male, circles = female, diamonds = unknown / unspecified sex; filled = affected, diagonal line = deceased, arrow = proband; double horizontal line = consanguinity.
How many generations should a pedigree chart cover?
Three generations from the proband is the minimum recommended; four is preferred where information is available.
How is a pedigree chart different from a family tree?
A family tree records relationships and lineage; a pedigree chart adds a defined symbol set encoding sex, affected status, deceased status, and other clinically relevant attributes.
Can a pedigree chart be drawn online?
Yes. Evagene draws pedigree charts in the browser using NSGC-compliant notation, with PDF / PNG / SVG and GEDCOM / CanRisk export.
What inheritance patterns can a pedigree chart show?
Autosomal dominant, autosomal recessive, X-linked dominant, X-linked recessive, Y-linked, and mitochondrial — suggestively. Confirmation requires molecular testing or formal segregation analysis.