Pedigree Chart
The Pedigree Chart is a reference tool covering pedigree chart, pedigree chart genetics, how to read a pedigree chart, pedigree chart template. Use the chart below to look up values instantly. Printable and downloadable versions are available on this page.
How to Read a Pedigree Chart
- Generations are labelled with Roman numerals (I, II, III) on the left side — Generation I is the oldest at the top and each subsequent generation is below.
- Squares represent males. Circles represent females. A diamond or unspecified shape is used when sex is unknown.
- A filled (shaded) shape indicates an affected individual — one who has the trait or condition being tracked. An unfilled (open) shape indicates an unaffected individual.
- A horizontal line between a male and female represents a mating or partnership. Vertical lines connect parents to their offspring. A horizontal line above a sibling group (sibship line) connects all children of the same parents.
- A dot inside a circle indicates a carrier female — someone who carries one copy of a recessive allele but does not show the trait. A half-filled shape indicates partial expression in conditions that show variable penetrance.
Pedigree Chart Symbols Reference
| Symbol Description | What It Represents | Used In |
|---|---|---|
| Unfilled square | Unaffected male | All pedigree types |
| Filled square | Affected male | All pedigree types |
| Unfilled circle | Unaffected female | All pedigree types |
| Filled circle | Affected female | All pedigree types |
| Circle with dot in centre | Carrier female (heterozygous) | Autosomal recessive and X-linked recessive pedigrees |
| Half-filled square or circle | Individual showing partial expression | Incomplete penetrance or dominance conditions |
| Square and circle connected by horizontal line | Mating pair — parents | All pedigree types |
| Double horizontal line between pair | Consanguineous mating (related individuals) | When relatives have children together — relevant for recessive trait analysis |
| Diagonal line through a shape | Deceased individual | When tracking traits across deceased relatives |
| Arrow pointing to a shape | Proband — the individual who first brought the family to medical attention | Clinical genetics pedigrees |
| Vertical line from mating line to sibling line | Offspring connection | All pedigree types |
| Small filled square or circle below sibling line | Stillbirth or miscarriage (depending on fill) | Clinical pedigrees |
Source: Bennett RL et al. — Standardised Human Pedigree Nomenclature — Journal of Genetic Counseling 2008
Inheritance Patterns Reference
| Inheritance Pattern | Key Features in the Pedigree | Example Conditions | Recurrence Risk |
|---|---|---|---|
| Autosomal Dominant | Trait appears in every generation (vertical transmission). Affected parent has approximately 50% affected children. Unaffected individuals do not carry the gene. | Huntington disease, Marfan syndrome, BRCA1/2 mutations | 50% chance of inheriting from an affected parent |
| Autosomal Recessive | Trait may skip generations. Both parents of an affected child are usually unaffected carriers. More common in consanguineous families. | Cystic fibrosis, sickle cell disease, PKU | 25% chance if both parents are carriers |
| X-linked Recessive | Almost always affects males. Carrier females are unaffected. Never passed from father to son (affected fathers pass X to daughters only). | Haemophilia A and B, Duchenne muscular dystrophy, colour blindness | 50% of sons of carrier mother are affected |
| X-linked Dominant | Affects both males and females but more severely in males. Affected father passes to all daughters, none of his sons. | Fragile X syndrome, Rett syndrome (de novo in most cases) | 50% of daughters of affected father are affected |
| Mitochondrial | Passes through mothers only — all children of an affected mother may be affected. Paternal inheritance never occurs. | Leber hereditary optic neuropathy, mitochondrial myopathies | 100% of children of affected mother may be affected (variable penetrance) |
Source: Thompson and Thompson Genetics in Medicine — standard genetics reference
Pedigree Analyzer
Enter family trait data across generations to auto-generate a pedigree diagram and identify the most likely inheritance pattern. Click any shape to cycle its status (Unaffected → Affected → Carrier) and use the sex toggle to change symbol type.
Click any shape to cycle status (Unaffected → Affected → Carrier). Click the arrow button to toggle sex.
II-sp is the external spouse of II-1. Their children appear in Generation III.
- Enter at least one affected individual to see pattern analysis.
Frequently Asked Questions
What is a pedigree chart?
A pedigree chart is a diagram that traces the inheritance of a specific trait or condition through multiple generations of a family. It uses standardised symbols (squares for males, circles for females, shading for affected individuals) to display family relationships and trait expression.
How do you determine the inheritance pattern from a pedigree?
Look for whether the trait appears in every generation (suggests dominant), skips generations (suggests recessive), primarily affects males (suggests X-linked recessive), or passes only through mothers (suggests mitochondrial). No single feature is definitive — combine multiple observations.
What does a carrier look like on a pedigree chart?
A carrier female for an autosomal recessive or X-linked recessive condition is typically shown as a circle with a dot in the centre. Male carriers for X-linked conditions (who would be unaffected) are less often specifically marked since they would simply be unaffected males connected to affected children through a carrier female.
What is autosomal recessive inheritance?
Autosomal recessive inheritance requires two non-functional copies of a gene (one from each parent) for the condition to appear. Parents who each carry one non-functional copy (carriers) appear unaffected but have a 25% chance with each pregnancy of having an affected child.
What is the proband in a pedigree?
The proband (also called the index case) is the individual in a family who first brought the family to medical or genetic attention — typically the affected person who prompted the clinical evaluation. They are indicated with an arrow in the pedigree.
Can pedigree charts be used in forensics?
Yes — pedigree analysis is used in forensic genealogy to reconstruct family relationships from DNA evidence. Law enforcement agencies use genealogical databases and pedigree reconstruction to identify unknown individuals from partial DNA matches in extended family networks.
What does a double line mean in a pedigree?
A double horizontal line between two individuals indicates a consanguineous mating — the couple are biologically related (cousins, for example). This is noted because consanguinity increases the risk of autosomal recessive conditions.
What is incomplete penetrance in a pedigree?
Incomplete penetrance means that some individuals who carry a dominant allele do not show the associated trait — they appear unaffected in the pedigree despite carrying the gene. This can make autosomal dominant patterns look irregular with apparent skipped generations.