Use a family tree when the claim is ancestry, a pedigree when the claim is inheritance of a trait or condition, and a genogram when the claim is a pattern inside a family system. The node shapes may look related, but the evidence, notation, privacy risk, and review standard are different.
The 30-second selection rule
Ask the sentence you want a reader to complete after viewing the diagram:
- “Now I can see who descended from whom and where the records came from.” → family tree.
- “Now I can see how a reported trait appears across biological relationships and generations.” → pedigree.
- “Now I can see which relational, health, and life-event patterns recur in this family system.” → genogram.
If the sentence contains two jobs, make two linked diagrams. Do not force genetics and emotional relationships into one legend simply because both use family structure.
Family tree: optimize for lineage and sources
A family tree can extend across many generations and include names, dates, locations, photographs, occupations, partnerships, and parentage. Its central evidence is genealogical: records, oral histories, archives, and documented relationships.
Minimum useful data:
| Field | Why it matters |
|---|---|
| Person identifier | separates people with similar names |
| Parent-child relationship | establishes lineage |
| Partnership or union | provides family context without implying parentage |
| Birth / death dates and places | distinguishes identities and chronology |
| Source per claim | shows which facts are documented, reported, or uncertain |
Mark adopted, step, foster, legal, and biological relationships according to the purpose and evidence. Do not collapse them into an unlabeled “parent” line if the distinction matters to the research question.
Pedigree: optimize for inheritance evidence
The National Human Genome Research Institute defines a pedigree as a chart that diagrams inheritance of a trait or health condition through generations and shows relationships plus trait status when known. The diagram is narrower than a family history archive: it prioritizes biological relationships, status for a defined trait, an index person when relevant, and a legend.
Minimum useful data usually includes:
- three generations where the purpose requires it;
- biological relationships and siblings in birth order;
- trait or condition definition;
- reported affected status and age of onset when known;
- testing status and result source when known;
- age or year of birth, and age and cause of death where relevant;
- proband or consultand marker where appropriate;
- recorder, historian, date, purpose, and legend.
The CDC notes that family health history reflects shared genes, behavior, and environment. A visual cluster is therefore not proof of a genetic cause. The pedigree organizes evidence for professional interpretation; it does not manufacture the evidence.
For a genetics or breeding task, use a specialist PedigreeMaker pedigree chart once the relationships, status labels, and uncertainty are explicit. Keep the output educational or documentary unless a qualified professional reviews the clinical interpretation.
Genogram: optimize for family-system patterns
A genogram starts with family structure and adds relational or contextual layers: closeness, conflict, cutoff, household transitions, repeated partnerships, major life events, caregiving, health concerns, or substance use. Those marks often represent reported experience or practitioner assessment rather than a civil record.
Minimum useful data:
- purpose and assessment date;
- people and structural relationships;
- household or union changes relevant to the question;
- the source of relationship-quality claims;
- dates or periods for events and relationship states;
- legend for every non-obvious line;
- explicit boundary between fact, report, and interpretation.
“Parent-child” and “emotionally close” are two different relationships. One should never substitute for the other.
One fictional family, three maps
Imagine Dana, their brother Lee, their parents, and two grandparents. The source packet contains birth certificates, an interview, and a health-history questionnaire.
Family tree output: names, parentage, birth years, places, and citations to records. The diagram may include grandparents’ immigration locations but no health shading.
Pedigree output: biological relationships, a clearly defined reported trait, ages of onset, testing status, and an index marker. Immigration details disappear unless directly relevant to the stated purpose.
Genogram output: the same structural family plus a reported cutoff between Dana and one parent, a close sibling tie, and a caregiving transition after a grandparent’s death. Trait shading may disappear unless it matters to the family-system assessment.
No diagram is “more complete.” Each removes data that does not support its claim.
Evidence labels that prevent overclaiming
Use a small status vocabulary beside the map or in a data table:
- documented: supported by a named record;
- reported: stated by a family member or historian;
- assessed: professional interpretation at a stated date;
- derived: calculated or structured from listed facts;
- unknown: not established;
- withheld: intentionally omitted for privacy.
Unknown is not unaffected. Unrecorded is not absent. A dashed line should never do five meanings at once.
Privacy changes with the diagram’s purpose
Family diagrams can expose information about people who did not create the record: health conditions, adoption, infertility, violence, sexuality, estrangement, or genetic testing. Apply minimum-necessary data, limit access, date the record, and follow the privacy and consent rules of the setting.
The 2022 NSGC practice resource specifically emphasizes confidentiality, a legend, recorder information, update date, and careful distinction of sex and gender in pedigree notation. That is a reminder that symbols are data claims, not decorative shortcuts.
Final decision checklist
- Write the one question the diagram must answer.
- Name the evidence source for every relationship and status.
- Choose one primary notation family.
- Define unknown, reported, derived, and assessed states.
- Remove data that does not serve the purpose.
- Create a second linked diagram when another purpose remains.
- State who must review the interpretation.
The right family diagram is not the one with the most symbols. It is the one whose claims a reader can identify, trace, and challenge.