Standard pedigree nomenclature is the visual shorthand genetic counselors and clinical geneticists use to record family history. The NSGC Pedigree Standardization Task Force (PSTF) publishes the canonical reference: Bennett et al. 1995, updated in 2008, and most recently reaffirmed and extended in 2022. The 2022 update is the current standard. The minimum standard for a clinical pedigree is three generations (proband, parents, and grandparents), with siblings, offspring, and pregnancies on each side.
| Symbol | Meaning |
|---|---|
| Square | Male (matches gender identity in current PSTF guidance) |
| Circle | Female (matches gender identity) |
| Diamond | Sex unknown / not disclosed, or nonbinary / gender-diverse without a binary identity |
| Triangle | Pregnancy (current or historical, regardless of sex) |
Transgender and gender-diverse individuals
The 2008 NSGC update, reaffirmed and clarified by the 2022 PSTF, directs that the pedigree symbol should reflect the individual's gender identity, not the sex assigned at birth or the karyotype. So a transgender woman is drawn as a circle and a transgender man as a square. Karyotype, hormonal status, or sex assigned at birth can be annotated below the symbol when clinically relevant (e.g., "46,XY" for a transgender woman in a hereditary cancer pedigree where Y-chromosome-related risks differ).
A diamond is reserved for individuals whose sex is unknown to the historian, or for a gender-diverse individual who does not identify within a binary framework. Don't use a diamond as a default symbol for transgender individuals; that is not current convention.
| Fill | Meaning |
|---|---|
| Empty (open) | Unaffected |
| Filled (solid) | Affected with the condition under study |
| Half-filled | Heterozygous carrier of an autosomal recessive condition (when carrier status is being depicted in the pedigree) |
| Dot in center | Obligate heterozygote (X-linked recessive carrier woman, or AR carrier deduced from offspring/parents) |
| Quartered fill | Used when tracking multiple conditions simultaneously: different quadrants represent different traits |
| ? inside symbol | Affected status unknown |
A diagonal slash through the symbol indicates the individual is deceased.
| Symbol | Meaning |
|---|---|
| Triangle (Δ) | Pregnancy (active or unspecified outcome) |
| Triangle with diagonal slash | Spontaneous abortion (SAB); annotate with gestational age if known |
| Triangle with diagonal slash + "TOP" | Termination of pregnancy |
| Square/circle with diagonal slash + "SB" | Stillbirth (≥ 20 weeks gestation, no signs of life) |
| Small filled square or circle | Neonatal death (use age and cause as annotation) |
Pregnancies are typically drawn smaller than postnatal individuals to make visual scanning easier.
- Proband (P): the affected individual through whom the family came to medical attention. Marked with a filled-in arrow pointing at the symbol, plus a "P" label.
- Consultand: the individual seeking counseling (may or may not be affected). Marked with an arrow pointing at the symbol, no "P" label. The consultand and proband may be the same person, or different people.
- Monozygotic twins: two symbols connected by sibship lines that meet at a single point, with a horizontal line drawn between the two symbols at the meeting point.
- Dizygotic twins: two symbols connected at a single point on the sibship line with no connecting horizontal line.
- Conjoined twins: connected at the body level, not just the sibship line.
- Twin zygosity unknown: connected at a single point with a "?" between them.
- Adopted into family: brackets
[ ]around the adopted individual, with dashed lines to adoptive parents and solid lines to biological parents (if known). - Adopted out of family: brackets
[ ]with dashed lines to biological parents. - Donor conception: "D" label for sperm or egg donor; gestational carrier (surrogacy) is labeled and connected with dashed lines distinguishing genetic vs gestational parentage. The 2022 PSTF includes expanded standards for assisted reproduction.
- Horizontal line between two symbols = relationship/partnership.
- Double horizontal line = consanguineous relationship.
- Diagonal short line through the relationship line = separation/divorce.
- Vertical line from a couple = offspring line, descending to the sibship line.
- Sibship line = horizontal line connecting all siblings, with vertical drops to each individual.
- Generations are labeled with Roman numerals (I, II, III) in the left margin; individuals within a generation are numbered left to right with Arabic numerals (II-1, II-2, II-3...).
The proband is the lowest generation when possible (i.e., the family is drawn upward and outward from the proband).
- Age: current age (or age at death) below the symbol, often abbreviated with "d." prefix for deceased (e.g., "d. 67").
- Diagnosis: abbreviated condition (e.g., "BC 42" = breast cancer at age 42) below the symbol.
- Genotype/karyotype: when relevant, listed below age/diagnosis (e.g., "BRCA1+", "46,XY").
- n=N: used inside a symbol to represent N siblings of the same sex/status not individually drawn.
- Transgender individuals are drawn with the symbol matching their gender identity (PSTF 2008, reaffirmed 2022). Karyotype is annotated below if relevant; it does not change the shape.
- Pregnancies are always triangles, regardless of whether sex is known.
- Diamond is for unknown sex or nonbinary identity, not the default for transgender individuals.
- Half-filled = AR carrier (or partial expression in a defined research context); dot in center = obligate heterozygote (different concept, deduced from inheritance, not directly tested).
- Three generations is the minimum standard for a clinical pedigree.
- Adoption uses brackets; dashed vs solid lines distinguish biological from social parentage.
- Consanguinity = double line between partners.
- Monozygotic twins have a horizontal line between them above the sibship junction; dizygotic do not.
- Bennett RL, Steinhaus KA, Uhrich SB, et al. Recommendations for Standardized Human Pedigree Nomenclature. Am J Hum Genet 1995.
- Bennett RL, French KS, Resta RG, Doyle DL. Standardized Human Pedigree Nomenclature: Update and Assessment of the Recommendations of the National Society of Genetic Counselors. J Genet Couns 2008.
- Bennett RL, French KS, Resta RG, Austin J. Standardized Pedigree Nomenclature Update Centered on Sex and Gender Inclusivity. J Genet Couns 2022. Current standard.