How to Draw a Pedigree Chart: A Complete Guide to Pedigree Drawing Software

What Is a Pedigree Chart?

A pedigree chart (also called a pedigree diagram or genogram) is a standardised graphical representation of a family's biological relationships across multiple generations. Unlike a simple family tree, which primarily shows names and lineage, a pedigree chart encodes clinically relevant information: biological sex, affected status for specific conditions, carrier status, consanguinity, pregnancy outcomes, and more.

Pedigree charts serve several critical functions in genetics and medicine:

• Pattern recognition — Identifying whether a condition follows autosomal dominant, autosomal recessive, X-linked, or mitochondrial inheritance.
• Risk assessment — Estimating the probability that an individual carries a pathogenic variant or will develop a condition, using models such as BRCAPRO, MMRpro, or the Claus model.
• Clinical documentation — Providing a concise, universally understood summary of a patient's family history that can be shared across clinical teams.
• Genetic counselling — Helping patients and families visualise their hereditary risks and understand how conditions are passed through generations.
• Research — Supporting linkage analysis, segregation analysis, and cohort studies where family structure is a key variable.

The utility of a pedigree chart depends entirely on the accuracy and consistency of its notation. For this reason, the genetics community has developed standardised symbol systems that are used worldwide.

Standard Pedigree Symbols and Notation

The symbols used in clinical pedigree charts are governed by recommendations from the International System for Human Cytogenomic Nomenclature (ISCN), the National Society of Genetic Counselors (NSGC), and the Pedigree Standardization Work Group. Gene names follow the HGNC (HUGO Gene Nomenclature Committee) conventions. Understanding these symbols is essential for anyone who draws or reads pedigree charts.

Individual Symbols

Relationship and Structural Lines

• Horizontal mating line — Connects two partners who have offspring together. A single horizontal line indicates a standard relationship.
• Double horizontal line — Indicates a consanguineous (blood-related) relationship between partners.
• Vertical descent line — Drops from the mating line to the sibship line, connecting parents to their children.
• Sibship line — A horizontal line from which siblings are suspended via short vertical lines.
• Adoption brackets — Square brackets around an individual on the sibship line indicate adoption into the family; brackets around the connection line indicate adoption out.
• Twins — Monozygotic (identical) twins are shown with their descent lines meeting at a single point, often with a horizontal bar. Dizygotic (fraternal) twins have separate descent lines that converge but do not meet.
• No offspring — A short vertical line from the mating line crossed with a horizontal bar indicates that the couple has no children.

Generational Numbering

Generations are labelled with Roman numerals (I, II, III, etc.) along the left margin, with Generation I at the top (the oldest generation). Individuals within each generation are numbered left to right using Arabic numerals. The proband in a three-generation pedigree might be designated as III-2, meaning the second individual in the third generation.

How to Draw a Pedigree: Step by Step

Whether you are drawing by hand or using software, the process of constructing a pedigree follows the same logical sequence. Here is a step-by-step approach used by genetic counsellors and clinical geneticists worldwide.

1. 1

   Identify the Proband

   Begin with the individual who prompted the genetic consultation or study. This person is marked with an arrow and is your starting point. In a clinical setting, this is typically the patient sitting in front of you; in a research context, it may be the index case that brought the family to attention.

2. 2

   Collect Family History

   Systematically gather information about at least three generations. For each family member, record: biological sex, current age or age at death, any relevant diagnoses (including age at diagnosis), genetic testing results, ethnicity, and consanguinity. Ask about miscarriages, stillbirths, and adopted individuals. Be thorough — the accuracy of downstream risk calculations depends entirely on the completeness of this data.

3. 3

   Establish the Generational Structure

   Arrange generations in horizontal rows. The oldest known generation goes at the top (Generation I). Label each row with its Roman numeral. Leave adequate vertical spacing between generations to accommodate descent lines and annotations.

4. 4

   Place Individuals Using Standard Symbols

   Draw each person using the correct ISCN symbol: squares for males, circles for females, diamonds for unknown sex. Fill or shade symbols according to affected status. Add the diagonal strike-through for deceased individuals and the central dot for obligate carriers.

5. 5

   Draw Relationship and Descent Lines

   Connect mating partners with a horizontal line. Drop a vertical line from the centre of the mating line to a horizontal sibship line, from which children are suspended. Use double lines for consanguineous unions. Position siblings left to right in birth order (eldest on the left).

6. 6

   Annotate Clinical Information

   Below or beside each symbol, add relevant clinical annotations: age, diagnosis, age of onset, genetic test results, and any other pertinent information. Use standardised abbreviations and HGNC gene symbols (e.g., BRCA1, MLH1, TP53) where applicable. Keep annotations concise to avoid cluttering the diagram.

7. 7

   Add a Legend and Date

   Include a legend if the pedigree uses shading patterns for multiple conditions (e.g., half-filled left for breast cancer, half-filled right for ovarian cancer). Record the date the pedigree was drawn and the name of the person who recorded it. In clinical settings, the pedigree becomes part of the medical record and must be attributable.

8. 8

   Review and Validate

   Double-check the pedigree for accuracy. Verify that all relationships are correctly represented, that affected status is assigned to the right individuals, and that no family members have been omitted. If using software with integrated risk models, this is the point at which you would run risk calculations to ensure the pedigree data produces sensible outputs.

Pedigree Drawing by Hand vs. Software

For decades, pedigrees were drawn exclusively by hand on paper or whiteboard. Many genetic counsellors still sketch preliminary pedigrees during patient consultations. Hand-drawing has its merits — it is immediate, requires no technology, and can be done anywhere. However, as clinical genetics has matured, the limitations of manual pedigree drawing have become increasingly apparent.

The consensus in clinical genetics is clear: while hand-drawn pedigrees remain useful for quick bedside sketches, any pedigree that becomes part of a clinical record, supports a risk assessment, or needs to be shared across a care team should be produced using dedicated pedigree software. The benefits of standards enforcement, integrated risk models, and structured data export far outweigh the learning curve of adopting a new tool.

What to Look for in Pedigree Drawing Software

Not all pedigree tools are created equal. When evaluating pedigree drawing software, consider the following capabilities:

How Evagene Approaches Pedigree Drawing

Evagene is a web-based pedigree management system designed for precision medicine. Its approach to pedigree drawing reflects a specific design philosophy: pedigree construction should feel as natural as sketching on paper, whilst producing clinically rigorous, standards-compliant output.

Freehand Gesture Drawing

Rather than relying exclusively on toolbar buttons or form-based input, Evagene supports freehand gesture recognition for pedigree construction. Draw a square on the canvas, and Evagene recognises it as a male individual. Draw a circle, and it becomes a female. Draw a line between two individuals, and the system infers the relationship type. This approach bridges the gap between the immediacy of hand-drawing and the precision of software — particularly useful during live patient consultations where speed matters.

Standard Notation and HGNC Compliance

Every symbol in Evagene conforms to ISCN/NSGC pedigree standards. Gene names follow HGNC nomenclature. The system enforces correct notation by design, meaning clinicians cannot accidentally produce non-standard pedigrees. Disease annotations draw from a catalogue of over 200 conditions with proper phenotype coding.

Keyboard Shortcuts

For users who prefer keyboard-driven workflows, Evagene provides extensive keyboard shortcuts for common pedigree operations: adding individuals, setting affected status, navigating between family members, and toggling annotations. This allows experienced users to construct complex pedigrees without lifting their hands from the keyboard.

Integrated Risk Models and Clinical Data

Evagene integrates BayesMendel risk models (BRCAPRO, MMRpro, PancPRO) directly into the pedigree interface. As family history data is entered, carrier probabilities and future cancer risk estimates update in real time. This tight coupling between pedigree data and risk calculation eliminates the error-prone process of manually transferring family history into a separate risk tool.

Data Exchange

Evagene supports GEDCOM import and export for interoperability with other pedigree and genealogy tools, as well as structured data export for research use. The platform is web-based and requires no installation.

For detailed documentation on Evagene's pedigree drawing capabilities, including tutorials and keyboard shortcut references, visit the Evagene help centre.

Comparing Pedigree Drawing Tools

Several pedigree drawing tools are available for clinical and research use. Each has its strengths, and the best choice depends on your specific workflow, institutional requirements, and budget. Here is a brief, honest comparison of the major options.

Frequently Asked Questions

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