Pedigree Chart Symbols: The Complete ACMG/NSGC Standard Guide

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Introduction to Standard Pedigree Symbols

A pedigree chart is a visual map of a family health history. It traces genetic traits, medical conditions, and biological relationships across multiple generations. Genetic counselors, clinical geneticists, and medical researchers rely on pedigree charts to evaluate hereditary disease risks and guide clinical care.

Without standard symbols, reading a family history drawn by another clinic would be confusing and error-prone. To solve this problem, the National Society of Genetic Counselors (NSGC) Pedigree Standardization Task Force published the official standardized human pedigree nomenclature. First established by Robin Bennett and colleagues in 1995, updated in 2008, and expanded in 2022 for sex and gender inclusivity, these rules define how every symbol, line, and annotation should be drawn.

This guide covers all standard pedigree chart symbols recognized by the NSGC and the American College of Medical Genetics and Genomics (ACMG). Whether you are preparing for board exams or managing patient charts, this manual provides clear rules, visual examples, and reference tables.

If you are learning how to quickly read family history charts, consult our practical tutorial on How to Read a Pedigree Chart in 5 Minutes. If you need to build a new tree from patient intake, follow our step-by-step guide on How to Create a Pedigree Chart, or explore our Master Inheritance Patterns Guide for full disease transmission rules.

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Basic Individual Symbols and Sex Assignment

Every pedigree chart begins with individuals represented by simple geometric shapes. The shape defines the biological sex or sex assigned at birth of the person.

Core Individual Symbols

• Male: Represented by a square.
• Female: Represented by a circle.
• Sex Unspecified or Unknown: Represented by a diamond. This symbol is used for early pregnancies where sex is unknown, for historical relatives whose sex was not recorded, or when sex is not relevant to the pedigree analysis.
• Deceased Individual: Indicated by a diagonal strike line passing through the symbol from top right to bottom left.

Sex Assignment and Gender Inclusivity (NSGC 2022 Update)

The 2022 NSGC practice resource update updated pedigree guidelines to clearly separate biological sex assigned at birth from gender identity:

1. Sex Assigned at Birth: Use standard square (male), circle (female), or diamond (unspecified).
2. Gender Identity Annotations: Write the individual's gender identity or transition status directly below or beside the symbol in text (for example, Transgender male, Transgender female, or Non-binary).
3. Gender Diverse Symbols: When an individual prefers a non-binary symbol representation, a diamond with explicit text notation is the standard clinical convention.

The vector diagram below shows the primary individual symbols used in standard medical pedigree charts:

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Disease, Carrier, and Genetic Testing Markings

Shading and interior markings convey clinical disease status, carrier genotypes, and genetic testing results.

Affected vs Unaffected Status

• Unaffected (Normal): Open, unshaded symbol with a white interior.
• Affected: Fully shaded, solid symbol (typically solid black or dark blue).
• Multiple Phenotypes: If a family has two different genetic conditions (for example, BRCA1 breast cancer and Lynch syndrome colorectal cancer), divide the symbol into quadrants or pie slices with distinct colors or cross-hatch patterns. Define each pattern clearly in the pedigree legend.

Carrier Status Symbols

Carrier symbols identify individuals who carry a disease-causing gene allele but do not show full clinical symptoms.

• Autosomal Recessive Carrier: Divided in half vertically, with the left half solid filled and the right half open.
• X-Linked Recessive Carrier: An open female circle containing a solid central dot.
• Obligate Carrier: An individual who does not show symptoms but must carry the gene based on pedigree logic (for example, an unaffected parent with an affected child and an affected parent). Indicated by a vertical line or half shading.
• Presymptomatic / Asymptomatic Carrier: An individual who carries a dominant disease gene (such as Huntington Disease) but has not yet reached the age of symptom onset. Represented by a single vertical line dividing the symbol.

Genetic Testing Status Annotations (*, E⁺, E⁻)

Documenting whether an individual has undergone molecular or chromosomal testing is a fundamental NSGC pedigree requirement:

• Tested Individual (*): An asterisk * is placed directly above or beside the symbol to indicate that genetic testing was performed.
• Tested Positive (E⁺): Labeled with E⁺ (Evaluated Positive) beside the symbol to indicate that the disease-causing mutation or variant was detected.
• Tested Negative (E⁻): Labeled with E⁻ (Evaluated Negative) beside the symbol to indicate that testing confirmed wild type alleles (no mutation detected).

The diagram below displays standard shading rules and genetic testing annotations:

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Proband, Consultand, and Indexing Conventions

Clear indexing ensures that anyone reading a pedigree chart can identify key family members and refer to specific individuals without confusion.

Identifying the Proband and Consultand

• Proband (Index Case): The affected individual who first brings the family to medical or genetic attention. Marked with a diagonal arrow pointing up and right toward the symbol, accompanied by the letter P.
• Consultand: The individual seeking genetic counseling or evaluation. The consultand may be unaffected (for example, a pregnant woman seeking risk assessment for a family history of cystic fibrosis). Marked with an arrow and the letter C.

Generation and Individual Numbering Rules

1. Generations: Numbered vertically using Roman numerals (I, II, III, IV) starting from the oldest generation at the top.
2. Individuals: Numbered horizontally within each generation from left to right using Arabic numerals (1, 2, 3, 4).
3. Individual Identifier: Combine the Roman numeral and Arabic numeral with a hyphen (for example, II-3 refers to the third person from the left in Generation II).

The diagram below illustrates standard proband notation and pedigree indexing:

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Relationship Lines and Consanguinity

Lines connect individuals on a pedigree chart to show partnerships, matings, and parental relationships.

Standard Relationship Types

• Relationship Line (Mating): A single horizontal line drawn between a male and a female at the same horizontal level.
• Separation or Divorce: A single horizontal relationship line marked with two diagonal hash marks (//) or a single slash through the line.
• Casual or Extramarital Relationship: Indicated by a horizontal line drawn with a dashed stroke.
• Consanguinity (Mating between blood relatives): Represented by a double horizontal line connecting partners who share a common ancestor (such as first cousins).

Consanguinity is a key risk factor in clinical genetics. It increases the probability that both parents carry the exact same rare autosomal recessive gene mutation inherited from a shared ancestor.

The diagram below highlights standard relationship lines and consanguineous partnerships:

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Sibships, Offspring, and Twins

Offspring are connected to parental relationship lines through vertical line drops that branch into a horizontal sibship line.

Sibship Order and Layout Rules

1. Birth Order: Siblings are placed along the sibship line in order of birth from left to right (oldest sibling on the far left, youngest sibling on the far right).
2. Line of Descent: A vertical line extends down from the middle of the parental relationship line to meet the horizontal sibship line.

Twin Symbols and Zygosity

Twins originate from a single point on the sibship line. The branches spread downward in a V shape:

• Dizygotic Twins (Fraternal): Two diagonal lines branch downward from a single point on the sibship line to two separate individual symbols (square/square, circle/circle, or square/circle).
• Monozygotic Twins (Identical): Two diagonal lines branch downward from a single point, joined by a horizontal connecting bar between the two branch lines.
• Unknown Zygosity Twins: Two diagonal lines branch from a single point, with a question mark (?) placed between the two lines.

The diagram below demonstrates how to draw fraternal twins, identical twins, and unknown zygosity twins:

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Pregnancy Loss, Miscarriages, and Stillbirths

Accurate recording of reproductive history is essential in genetic counseling. Pregnancy loss can reveal recessive lethal conditions, chromosomal translocation burdens, or structural abnormalities.

Reproductive Loss Symbol Standards

• Spontaneous Abortion (Miscarriage): Represented by a small triangle, labeled SAB.
• Termination of Pregnancy (Induced Abortion): Represented by a small triangle with a diagonal slash through it, labeled TOP.
• Stillbirth: Represented by a standard symbol containing a diagonal strike line, labeled SB with gestational age (for example, SB 32 wks).
• Ectopic Pregnancy: Represented by a small triangle labeled ECT.

The diagram below illustrates standard symbols for reproductive history and loss:

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Assisted Reproductive Technologies (ART) and Adoption

Modern medical pedigree charts frequently document donor gametes, surrogacies, and adoptions. Standard NSGC pedigree nomenclature uses precise symbols to distinguish biological parentage from legal or social parentage.

Assisted Reproductive Technology (ART) Conventions

In ART scenarios, letter identifiers inside or beside symbols indicate genetic and gestational roles:

• D: Donor of sperm or ovum (Egg).
• S: Surrogate (Gestational carrier only, with no genetic contribution).
• Sperm Donor: The rearing mother and a Sperm Donor (D square) connect to the pregnancy or child (P).
• Ovum Donor: The rearing father and an Ovum Donor (D circle) connect to the child (P).
• Surrogate Only: Biological parents connect with solid lines to the child (P), while a surrogate (S circle) carries the pregnancy.
• Surrogate Ovum Donor: The surrogate also provides the egg (D circle), connecting with the biological father to the child (P).
• Planned Adoption / Donor Embryo: Sperm donor (D square) and egg donor (D circle) connect with solid lines to the child in brackets [P], while rearing parents connect with a dashed line.

The diagram below illustrates standard NSGC symbols for reproductive technology scenarios:

Adoption Conventions: Adopted Out vs Adopted Into Family

Adoption status is represented by enclosing the individual's symbol in square brackets [ ]. The type of line extending upward defines whether the adoption is into or out of the biological family:

• Adopted Out of Family: Enclosed in square brackets [ □ ] or [ ○ ] with a solid line extending upward to the biological parents.
• Adopted Into Family: Enclosed in square brackets [ □ ] or [ ○ ] with a dashed line extending upward to the adoptive parents.

The diagram below highlights the standard NSGC adoption symbols: