A pedigree chart maps a trait or condition across multiple generations of a family using standardized symbols and connecting lines. Whether you’re completing a genetics assignment or documenting your family’s medical history, the process follows the same basic steps: gather health information, choose your symbols, start with one key person, and build outward generation by generation.
What You Need Before You Start
A pedigree is only as useful as the data behind it. Before drawing anything, collect health details for as many blood relatives as possible: parents, siblings, half-siblings, grandparents, aunts, uncles, nieces, and nephews. For each person, you want to know their major medical conditions, the age they were diagnosed, their cause of death (if applicable), their age at death, and their ethnic background. Even “nothing notable” is worth recording, because unaffected individuals help establish inheritance patterns just as much as affected ones do.
If you’re building a chart for a class, your textbook or assignment will typically specify which trait to track. If you’re documenting real family history, focus on conditions that recur across relatives, such as heart disease, cancer, diabetes, or known genetic disorders.
Standard Pedigree Symbols
Pedigree charts use a universal set of shapes so anyone trained in genetics can read them at a glance:
- Square: male
- Circle: female
- Diamond: sex unspecified or unknown
- Filled (solid) shape: affected by the trait or condition being tracked
- Open (empty) shape: unaffected
- Half-filled shape: carrier of a recessive trait (shows no symptoms but carries one copy of the gene)
- Diagonal line through a shape: deceased
- Horizontal line between two shapes: mating or partnership
- Double horizontal line: consanguineous relationship (the partners are blood relatives)
- Vertical line descending from a partnership line: offspring
- Horizontal line above siblings with vertical drops to each: sibship line
These conventions were first standardized in 1995 and most recently updated in 2022 by the National Society of Genetic Counselors. The 2022 revision clarified how to distinguish between sex assigned at birth and gender identity on a chart, ensuring inclusive documentation for transgender and gender-diverse individuals without introducing new symbols. If this distinction matters for your chart, note gender identity in text beside the symbol while using the shape that corresponds to the person’s chromosomal sex, since that’s what determines inheritance patterns.
Step 1: Draw the Proband
Start with the proband, the first person in the family who brought the condition to attention (or, in a school assignment, the individual the problem specifies). Draw a filled square or circle in the center of your page. Place a small arrow pointing to the lower left corner of the symbol to mark this person as the proband. Starting in the middle gives you room to expand upward for older generations and downward for younger ones.
Step 2: Add the Parents
Draw the proband’s parents one row above. Place the father (square) on the left and the mother (circle) on the right, or vice versa, as long as you stay consistent. Connect them with a single horizontal line. Draw a vertical line descending from that partnership line down to the proband. If the parents are related to each other, use a double horizontal line instead and note the degree of relation above it (for example, “first cousins”).
Fill in or leave open each parent’s symbol depending on whether they show the trait. If a parent is a known carrier but unaffected, use a half-filled symbol.
Step 3: Add Siblings
Draw the proband’s brothers and sisters along the same horizontal row, arranged from oldest on the left to youngest on the right. Connect all siblings with a horizontal sibship line above their symbols, with short vertical lines dropping down from it to each individual. Leave some horizontal space next to each sibling so you can later add their partners and children if needed.
For twins, draw two vertical lines from the same point on the sibship line. If the twins are identical (monozygotic), connect those two lines with a small horizontal bar. If they are fraternal (dizygotic), leave the lines separate but originating from the same point.
Step 4: Build Outward
Now expand the chart generation by generation. Add grandparents one row above the parents, connecting each pair with a horizontal partnership line and drawing a descent line to their child (the proband’s parent). Add aunts and uncles as siblings of the relevant parent, following the same left-to-right birth order convention.
If you have information on the proband’s children or the children of siblings, add a new row below. Each generation gets its own horizontal level on the chart. Label generations with Roman numerals along the left side (I for the oldest generation at the top, II for the next, and so on). Within each generation, number individuals from left to right with Arabic numerals. This lets you refer to any person quickly, like “individual III-2” for the second person in the third generation.
Notations and Details
Below or beside each symbol, add relevant medical details. Common annotations include age or year of birth, age at diagnosis of the tracked condition, cause of death, and the abbreviation “d.” followed by the age at death. Keep these brief. A typical annotation might read “dx 42, breast ca” for a person diagnosed with breast cancer at age 42.
A few other situations have their own conventions. Adopted individuals get brackets around their symbol, with “A in” or “A out” to show whether they were adopted into or out of the family. A pregnancy in progress is shown as a small triangle. A miscarriage is a small triangle with a diagonal line. If someone’s affected status is unknown, use a question mark inside the symbol.
Include a legend in one corner of the chart that defines what a filled symbol means, what any half-filled or patterned symbols represent, and any abbreviations you used. Even with standardized symbols, a legend removes ambiguity, especially when tracking more than one condition at a time (in which case different fill patterns or colors distinguish the conditions).
Reading Inheritance Patterns
Once your chart is complete, the visual pattern of filled symbols across generations tells you a lot about how the trait is inherited.
If the trait appears in every generation and affects both males and females in roughly equal numbers, it likely follows an autosomal dominant pattern. A person only needs one copy of the gene variant to show the trait, so at least one parent of every affected individual will also be affected.
If the trait skips generations, appearing in grandchildren but not their parents, it’s more likely autosomal recessive. Both parents can be unaffected carriers, and roughly one in four of their children will be affected. You’ll often see unaffected parents producing affected offspring.
If the trait overwhelmingly or exclusively affects males, consider X-linked recessive inheritance. Because males have only one X chromosome, a single copy of the variant is enough to produce the trait. Females, with two X chromosomes, would need two copies and are more often unaffected carriers. A classic clue is an unaffected mother who has affected sons but no affected daughters.
Digital Tools for Pedigree Charts
You can absolutely draw a pedigree by hand on graph paper, and many genetics courses expect exactly that. But if you need a polished digital version, several tools can help:
- QuickPed: A free web app designed specifically for pedigree charts. You build the family interactively and can save the result as an image or in PED format for genetic analysis software.
- TrakGene: Geared toward genetic counselors, with built-in clinical terminology and risk assessment features. More powerful than you need for a class assignment, but useful for medical documentation.
- SmartDraw: A general diagramming tool with pedigree templates and a library of genetic symbols. Good if you want more control over layout and design.
- Visual Paradigm: Another online diagramming platform with drag-and-drop pedigree chart tools.
For a school project, QuickPed is the easiest starting point since it’s free, requires no download, and enforces standard pedigree conventions automatically. For clinical or professional use, TrakGene offers deeper integration with genetic counseling workflows.
Common Mistakes to Avoid
The most frequent error is inconsistent symbol use, such as switching which side the father appears on or mixing up filled versus half-filled symbols. Pick a convention and stick with it across the entire chart. Another common mistake is forgetting to include unaffected relatives. Skipping healthy family members makes it impossible to determine inheritance patterns accurately, because the ratio of affected to unaffected individuals is what reveals whether a trait is dominant, recessive, or sex-linked.
Spacing problems also trip people up. If you start drawing in a corner, you’ll run out of room fast. Begin with the proband near the center of your page and sketch lightly at first. Three generations is the minimum for most purposes, and a three-generation chart with aunts, uncles, and cousins can easily include 15 to 25 individuals.