TEMPLATE

Three-Generation Pedigree

A classic three-generation classroom pedigree. Grandparents are at the top, their children in the middle row, and grandchildren at the bottom. The proband (the person whose trait history is being studied) is marked with the standard arrow and labeled P. The affected grandfather shows that a trait can enter the chart from the older generation.

Inheritance pattern & biological mechanism

The three-generation pedigree represents the gold standard in clinical genetics, primary care health assessments, and introductory genetics education. It captures the proband’s generational peers, their parental generation, and the grandparental lineage, providing sufficient statistical depth to evaluate dominant, recessive, and sex-linked hypotheses.

Key transmission rules

Each horizontal tier corresponds to an integer generation numbered with Roman numerals (I, II, III).
Individuals in each tier are numbered sequentially from left to right (e.g. I-1, I-2, II-1, II-2) to allow precise clinical documentation.
Transmission patterns can be verified across two full reproductive transitions (grandparents to parents, parents to children).
The proband arrow identifies the consultand or affected individual who prompted the genetic evaluation.

Representative real-world conditions

Hereditary Breast and Ovarian Cancer (HBOC)

BRCA1, BRCA2 genes

Three-generation pedigrees reveal early-onset breast, ovarian, or pancreatic cancer across maternal or paternal relatives.

Lynch Syndrome (HNPCC)

MLH1, MSH2, MSH6, PMS2

Evaluates families against the Amsterdam II criteria by checking for colorectal and endometrial cancer across multiple generations.

Familial Hypercholesterolemia

LDLR, APOB, PCSK9

Captures premature coronary artery disease, heart attacks, and xanthomas across three continuous tiers.

How to analyze this chart

1
Generation I: Grandfather Arthur (I-1) is affected by the trait of interest and partnered with unaffected grandmother Beatrice (I-2).
2
Generation II: Arthur passes the allele to his son Charles (II-1), while son George (II-3) does not express the condition. Charles partners with unaffected Diana (II-2).
3
Generation III: Charles and Diana have two children: an affected son Evan (III-1), designated as the proband with an arrow, and an unaffected daughter Fiona (III-2).
4
The vertical progression Arthur (I-1) → Charles (II-1) → Evan (III-1) provides a direct line demonstrating paternal transmission.

Diagnostic checklist: confirming vs ruling out

Confirming clues

✓ Direct parent-to-child transmission spanning from Generation I to Generation III.
✓ Male-to-male transmission (Arthur to Charles, Charles to Evan), proving the gene is not X-linked.
✓ Both affected and unaffected siblings in Generation II and Generation III, consistent with single-gene segregation.

Caveats & ruling out

⚠ If the trait were mitochondrial, Arthur (an affected male) could not have passed it to Charles.
⚠ If the trait were X-linked recessive, Arthur could not pass his affected phenotype to his son Charles because fathers only contribute their Y chromosome to sons.

Frequently asked questions

Why is a three-generation pedigree the preferred medical standard?

Three generations provide enough data to differentiate autosomal dominant, autosomal recessive, and sex-linked inheritance while remaining practical to collect from patient recall during an appointment.

What is the difference between a proband and a consultand?

A proband is the affected individual through whom the family came to attention. A consultand is the person seeking genetic counseling or evaluation, who may be affected or an unaffected relative seeking risk assessment.

How should I record age of onset or death in this template?

You can add notes and labels beneath each individual in the editor inspector to specify exact diagnosis age, current age, or year and cause of death.

Blank Pedigree Chart

A clean canvas to build any pedigree from scratch.

Autosomal Dominant Pedigree

Trait appears in every generation; one affected parent usually has affected children.

Autosomal Recessive Pedigree

Unaffected carrier parents can have an affected child; the trait may skip generations.