Pedigree symbols reference: a complete guide to standard notation

Short version. A clinical pedigree uses a small, tightly-defined vocabulary of symbols: squares for male individuals, circles for female, diamonds for unknown or non-disclosed sex, filled shapes for affected status, a centre dot for known carriers of a recessive condition, an arrow for the proband, brackets for adoption, a double horizontal line for consanguineous unions, and specific conventions for twins, pregnancy, and reproductive loss. The reference below covers every symbol in the 2022 National Society of Genetic Counselors (NSGC) standard (Bennett et al.), with ASCII diagrams and notes on the clinical situations each symbol encodes.

The canonical sources are Bennett, Steinhaus, Uhrich, O'Sullivan, Resta et al. (1995) American Journal of Human Genetics; Bennett, French, Resta, and Doyle (2008) Journal of Genetic Counseling; and Bennett, French, Resta, and Austin (2022) Journal of Genetic Counseling. The 2022 update introduced gender-inclusive symbols and clarified terminology around reproductive loss without deprecating the established core vocabulary.

Individual symbols: sex and identity

Every individual on a pedigree is drawn as a geometric shape whose form encodes sex or gender status, whose fill encodes affected status, and whose position encodes generation and sibship. The three shapes in common use are the square, the circle, and the diamond.

  Male            Female          Unknown / Non-disclosed
  ┌───┐             ╭───╮                  ◇
  │   │            │     │                ╱ ╲
  └───┘             ╰───╯                ◇   ◇

The diamond is used for (a) an individual whose sex is not known to the informant (common in distant relatives), (b) an individual who does not disclose sex or gender, or (c) an unborn fetus whose sex has not been determined. In reproductive and fetal-loss documentation, a smaller diamond denotes a pregnancy loss; a larger diamond denotes a living individual.

Transgender status, when clinically relevant, is marked by recording the sex assigned at birth with a small inner shape and the current gender identity with the outer shape, or by annotation. The 2022 NSGC update provides language for these conventions and emphasises that documentation should follow the individual's preference where possible.

Affected status and multiple conditions

Affected status is shown by filling the shape. A fully filled (black) shape means the individual is affected by the index condition. An unfilled shape means the individual is unaffected or of unknown status (the two are sometimes distinguished by a question mark inside the shape where status is explicitly unknown).

  Unaffected       Affected         Carrier (heterozygote)
  ┌───┐            ■■■■■               ┌───┐
  │   │            ■■■■■               │ ● │
  └───┘            ■■■■■               └───┘

  Multiple conditions (shape divided into quadrants):
       ┌─┬─┐     Upper-left  = cancer
       │■│ │     Upper-right = mental health
       ├─┼─┤     Lower-left  = cardiovascular
       │ │■│     Lower-right = metabolic
       └─┴─┘     (Key always shown on chart)

A centre dot denotes a known heterozygous carrier of an autosomal recessive condition. For X-linked conditions, a centre dot in a female shape denotes an obligate or known carrier. An obligate carrier may also be inferred from pedigree structure (the daughter of an affected X-linked recessive father is obligately a carrier), in which case some services annotate with "OC".

Where a pedigree tracks two or more conditions, the shape is subdivided into quadrants and a legend on the chart maps each quadrant to a condition. Four is the practical maximum; beyond that, affected conditions are recorded in the individual's annotation pane rather than visually.

Deceased, proband, and consultand

A deceased individual is marked with a diagonal line through the shape, typically from upper-right to lower-left. The age at death and cause of death, if known, are recorded beneath the shape.

  Deceased              Proband              Consultand
  ┌───┐                  ┌───┐                 ┌───┐
  │ ╲ │                  │   │                 │   │
  └───┘                  └───┘                 └───┘
     ╲                   ↙                      ↙ P
                      (arrow)                (arrow + P)
  d. 2014 / MI       III-4 (proband)       III-6 (consultand)

The proband (index case) is the first affected individual to come to medical attention in the family — marked by an arrow pointing to the lower-left of the shape. The consultand is the person who sought genetic counselling, who may or may not be the proband. Where consultand and proband differ, the arrow marks the proband and the consultand is marked separately, often with the letter P.

Reproductive outcomes: pregnancy, loss, termination

Reproductive outcomes require specific symbols because the clinical interpretation — recurrence risk counselling, karyotype inference, preventive management — depends on reading them correctly.

  Spontaneous       Stillbirth         Termination       No children
  abortion
      ▽              ┌───┐                 ▽                  ─┬─
                     │ ╲ │                ╱ ╲                  ║
   (12 wks)          └───┘               ─────                 ║
                  SB 36 wks          TOP 14 wks / T21

Twins and multiple births

Twin pairs branch from a single point on the sibship line. The shape of the branching encodes zygosity.

  Monozygotic twins     Dizygotic twins     Zygosity unknown
         │                     │                   │ ?
         •                     •                   •
        ╱ ╲                   ╱ ╲                 ╱ ╲
      ┌───┐┌───┐            ┌───┐┌───┐         ┌───┐┌───┐
      │   ├┤   │            │   ││   │         │   ││   │
      └───┘└───┘            └───┘└───┘         └───┘└───┘
     (horizontal         (no connector)     (? above vertex)
      bar joining)

Monozygotic twins are joined by a horizontal bar between their shapes. Dizygotic twins are drawn without the bar. When zygosity has not been determined, a question mark is placed above the meeting point. Higher-order multiples (triplets, quadruplets) extend the same convention — three or four lines meeting at a single point.

An evaluated twin — the twin whose clinical phenotype is the reason for the consult — is marked with a small "e" or labelled in the annotation pane, particularly in discordant monozygotic twin studies.

Relationships: mating, consanguinity, separation

Horizontal lines connect individuals in a partnered relationship. Vertical lines descend from the relationship line to a sibship line, from which individual shapes branch. The specific style of the horizontal line carries meaning.

  Mating (couple)        Consanguineous           Separated
  ┌───┐───╭───╮         ┌───┐═══╭───╮         ┌───┐─╱─╭───╮
  │   │   │   │         │   │   │   │         │   │   │   │
  └───┘   ╰───╯         └───┘   ╰───╯         └───┘   ╰───╯

  Divorced              No children
  ┌───┐─╱╱─╭───╮        ┌───┐───╭───╮
  │   │    │   │        │   │   │   │
  └───┘    ╰───╯        └───┘   ╰───╯
                            ═══  (double line below; "no children by choice")

A double horizontal line between two partners denotes consanguinity — the partners share one or more recent common ancestors. This is clinically critical because consanguineous unions carry a higher prior probability of autosomal recessive conditions in offspring. A single slash across the mating line denotes separation; a double slash denotes divorce. An unknown parent is drawn as a diamond without connection to a wider family structure.

Adoption: biological versus adoptive relationships

Adoption is shown with brackets around the adopted individual's shape. The lines connecting the shape to the rest of the family distinguish biological from adoptive relationships.

  Adopted into family       Adopted out of family
      [┌───┐]                    [┌───┐]
      [│   │]                    [│   │]
      [└───┘]                    [└───┘]
        │ ┆                        │ ┆
     (solid to           (solid to biological
      adoptive;              parents;
      dashed to             dashed to adoptive)
      biological)

The convention is: solid lines connect biological relationships, dashed lines connect adoptive relationships. Brackets around a shape indicate that individual was adopted. When both sets of parents are shown, the two lines (biological and adoptive) clearly distinguish which is which. For clinical purposes, recurrence risks are calculated from the biological line; adoptive relationships are recorded for family context but do not propagate genetic risk.

Complete symbol table: quick reference

Common annotations: what goes next to each shape

Alongside the symbol itself, short annotations record clinically critical information. Conventions differ between services, but a widely used ordering is:

• Line 1 (inside the shape): generation-individual identifier, e.g. III-4
• Line 2 (below shape): name or initials
• Line 3: current age, or "d." with age at death
• Line 4: affected status phenotype, age at onset, e.g. "BrCa, dx 47"
• Line 5: test results and variant nomenclature where reported, e.g. "BRCA1 c.5266dupC, pathogenic"

Age of onset is clinically critical for age-dependent penetrance calculations in Bayesian risk models. BRCAPRO, for instance, weights an unaffected older female relative quite differently from an unaffected younger relative, and the model cannot do its job without that age annotation. See our cancer risk assessment guide for how ages propagate through the models.

How Evagene supports this

Evagene enforces NSGC 2022 symbol conventions automatically — users do not select or pick from a symbol palette. When a clinician records the sex of an individual, the shape is chosen; when they record affected status for a condition, the fill is applied according to the condition's legend entry; when they record a consanguineous relationship, the line is doubled; when twins are recorded with known zygosity, the correct branching style is drawn. This removes a category of notation errors that arise when users are given a drag-and-drop palette of pre-drawn symbols.

For services that record multiple conditions on a single pedigree, Evagene's quadrant-fill logic scales with the 200+ disease catalogue and emits a consistent legend per chart. Where an individual is affected by more than four conditions, the additional conditions are recorded in the individual's annotation pane and cross-referenced to the chart legend. Consanguinity is detected automatically from pedigree structure where individuals are entered as related, and Wright's coefficient of inbreeding is computed in the background for any downstream use in recessive-disease risk calculations.

Exported pedigrees (PDF, PNG, SVG, GEDCOM) retain NSGC-compliant notation. For embedded usage via the iframe or SVG viewer, the same rules apply — an embedded chart shown in a patient portal uses the same symbols a clinician would draw. Our pedigree drawing software guide describes the live-drawing interface in more depth.

Frequently asked questions

Related reading

• Standard pedigree nomenclature and the NSGC timeline
• Pedigree chart examples with inheritance patterns
• How to make a pedigree chart in 5 steps
• Pedigree drawing software
• Clinical genetics pedigree tools
• Hereditary cancer risk assessment