Pedigree Symbols and Notation, Fully Explained

Pedigree charts serve as a universal clinical and scientific language across genetics, medicine, and evolutionary biology. Standardized pedigree nomenclature—codified by the National Society of Genetic Counselors (NSGC) Pedigree Standardization Task Force—ensures that genetic risks, relationships, and health conditions can be interpreted unambiguously by any healthcare professional worldwide.

Below is the definitive reference for standard pedigree notation, organized by clinical context.

1. Individuals and gender notation

Basic geometric symbols represent biological sex and gender identity:

Symbol	Medical Definition	Clinical Notes
Square	Male	Designated based on chromosomal, phenotypic, or legal male status.
Circle	Female	Designated based on chromosomal, phenotypic, or legal female status.
Diamond	Sex unknown or unspecified	Used for early fetuses, undisclosed gender, or undocumented ancestors.
Diamond with ‘P’	Ongoing pregnancy	Accompanied by estimated gestational age (e.g. “LMP: 14w”).
Symbol with number	Multiple siblings or individuals	A number inside a symbol (e.g. circle with ‘4’) indicates four unaffected sisters.
Square/Circle with interior diamond	Transgender or gender-diverse individual	Outer shape represents gender identity; inner diamond indicates birth sex.

2. Disease and trait status notation

Shading and interior markings convey phenotypic status, genetic carrier states, and diagnostic findings:

Marking	Phenotypic Status	Interpretation
Solid shading	Clinically affected	The individual expresses diagnostic symptoms of the trait or disease.
Central dot	Obligate or tested carrier	Heterozygous carrier for an autosomal recessive or X-linked recessive gene.
Half-shading (vertical)	Presymptomatic / Asymptomatic gene carrier	Tested positive for a pathogenic dominant variant without manifesting symptoms.
Quadrant / Sector shading	Multiple conditions	A symbol split into 2 or 4 sectors, each color-coded to a distinct condition in the legend.
Diagonal slash (bottom-left to top-right)	Deceased	Accompanied by age at death (e.g. “d. 72y”) and primary cause of death.
Arrow pointing to symbol with ‘P’	Proband	The primary affected individual through whom the family came to clinical attention.
Arrow without ‘P’	Consultand	The individual seeking genetic counseling or evaluation (may be affected or unaffected).

3. Reproductive losses and assisted reproduction

Capturing pregnancy losses is critical in medical genetics, as recurrent miscarriages often signal chromosomal translocations or lethal recessive alleles:

• Spontaneous abortion (miscarriage): A small solid triangle without gender specification. If chromosomal or phenotypic sex was determined by autopsy or karyotyping, a small square or circle is used instead, marked with gestational age.
• Termination of pregnancy (TOP): A small triangle with an intersecting diagonal slash.
• Stillbirth (gestational age ≥ 20 weeks): A square or circle with a diagonal slash, labeled with the abbreviation SB and the gestational age in weeks.
• Donor gametes (sperm/egg donor): A horizontal line originating from a letter ‘D’ or annotated symbol, indicating third-party reproductive contribution.
• Surrogate carrier: Dashed lines connecting the fetus/child to a gestational carrier bracketed separately from genetic parents.

4. Relationship and descent lines

Connecting lines establish biological, legal, and multi-gestational kinship:

• Single horizontal line: A reproductive partnership or marriage.
• Double horizontal line: A consanguineous union (partners who share a common biological ancestor, such as first or second cousins). This substantially elevates the risk of homozygous recessive conditions in offspring.
• Single or double slash through union line: Separation (single slash) or legal divorce (double slash).
• Vertical descent line: Traces direct biological parentage down to offspring.
• Horizontal sibling line (sibship bar): Connects children of the same union, arranged strictly in chronological birth order from left to right.
• Twin branches (shared vertex): Two diagonal descent lines originating from a single point on the sibship bar.
  • Monozygotic (identical) twins: Connected by a horizontal bar between the diagonal branches.
  • Dizygotic (fraternal) twins: Lack the horizontal connector bar.
  • Unknown zygosity: A question mark (?) placed inside the branch vertex.
• Dashed lines & brackets [ ]: Denotes adoption. Brackets enclose the individual symbol, with a solid line connecting to birth parents (if known) and a dashed line connecting to adoptive parents.

Standard generational numbering conventions

To eliminate confusion when discussing multi-generational charts during clinical grand rounds, pedigrees follow a standardized coordinate numbering grid:

1. Generations are labeled with Roman numerals (I, II, III, IV, etc.) placed in the left margin, starting with the earliest documented generation at the top.
2. Individuals within each generation are numbered with Arabic numerals (1, 2, 3, etc.) from left to right across the entire tier.
3. Every person possesses an unambiguous clinical address: individual II-3 refers to the third person from the left in Generation II.

The mandatory chart legend

A pedigree without an explicit legend is clinically unusable. Standards require every pedigree chart to include:

• A key defining each fill color, pattern, and symbol used.
• Names of all conditions or traits tracked.
• The date of documentation and the author’s initials or credentials.
• The family surname or clinical identification code.

Frequently asked questions

What is the difference between classroom legacy notation and modern clinical notation?

In classical biology textbooks, heterozygous carriers are frequently drawn with a half-shaded symbol. Modern clinical genetics standards reserve half-shading for presymptomatic dominant gene carriers and use a central dot for recessive carriers. Our chart maker lets you switch between clinical and legacy notation with a single toggle in project settings.

How do you record consanguinity between distant relatives?

If a couple shares a common great-grandparent, draw the ancestral branches ascending to the shared ancestors so the biological loop is closed, and render the partnership line as a double line.

Can a pedigree include multiple medical conditions simultaneously?

Yes. Standard clinical practice divides symbols into quadrants or sectors, or applies distinct color tints. For example, left-half shading can represent breast cancer while right-half shading represents ovarian cancer, clearly illustrating hereditary cancer syndrome overlap.

Practice standard notation

To inspect these symbols in live, interactive projects, open our twins template for zygosity notation, the adoption template for bracketed descent, or our example charts page to view full case studies.

If you are just getting started, read our primer on what is a pedigree chart, follow our practical how-to tutorial, or explore our interactive symbols guide.

Make your own chart — free, no sign-up →

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