Pedigree

Biology • Mendelian Genetics

Written by STEM Calculators Team Published January 9, 2026 Updated February 24, 2026

Pedigree toolkit

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Rule-based suggestion only: this mode ranks likely inheritance patterns using heuristic checks (not a definitive diagnosis). Add family members, then click Suggest.

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Keep IDs short to reduce label crowding in the chart.

Sex

Affected Filled shape

Mother (optional)

Father (optional)

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CSV columns: id,sex,affected,mother,father (sex = M/F; affected = 0/1; mother/father are IDs or blank).

Family members

ID	Sex	Affected	Mother	Father
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Legend

In “Suggest pattern”, hover individuals to see details. In “Compute risk”, hover bars for exact probabilities.

Choose a mode, enter data, then run the calculation.

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Pedigree: pattern suggestion and offspring risk

A pedigree is a family diagram used to track a trait across generations. This calculator focuses on two practical tasks: suggest a likely inheritance pattern and compute child risk given a chosen model.

The “Suggest pattern” output is rule-based and should be treated as a hint, not a diagnosis.

Pedigree symbols and conventions

Square = male, circle = female.
Filled shape = affected; unfilled = unaffected.
Parents connect to children through a relationship line; children are usually drawn one generation below.
In X-linked traits, sex matters because sons receive their X chromosome from the mother, while daughters receive one X from each parent.

Core inheritance models used in the calculator

Model	Typical pedigree clues	Common “tell” features
Autosomal dominant (AD)	Trait often appears in every generation (vertical transmission).	Male-to-male transmission can occur (father → son), which argues against X-linked patterns.
Autosomal recessive (AR)	Trait may skip generations. Two unaffected parents can have an affected child if both are carriers.	Similar frequency in males and females (usually no strong sex bias).
X-linked recessive (XLR)	Often more affected males. Carrier females can have affected sons.	No male-to-male transmission. Affected females are rarer and often require an affected father plus a carrier/affected mother.
X-linked dominant (XLD)	Vertical pattern, but inheritance depends on sex.	If a father is affected, all daughters are affected (he passes his X to every daughter) and no sons inherit the trait from him (he passes Y to sons).

Real pedigrees can be messy (small families, incomplete information, de novo mutations, reduced penetrance). The calculator uses the “clean textbook” assumptions above.

Mode A — Inheritance pattern suggestion (heuristic)

The “Suggest pattern” mode extracts simple features from your pedigree entry and assigns a score to each model. Examples of features include:

Generation skipping: an affected child with two unaffected parents (supports recessive).
Male bias: more affected males than females (supports X-linked recessive).
Male-to-male transmission: father → son affected (supports autosomal; contradicts X-linked).
Affected father → all affected daughters: supports X-linked dominant.

Because the rules can conflict in small pedigrees, the output is a ranked list, not a single “answer.”

Mode B — Offspring risk calculator (probability)

In risk mode, you select a model and define the parents’ statuses. The calculator then computes: P(affected child) and, when relevant, P(carrier child).

Autosomal recessive example (carriers)

If both parents are carriers: \(Aa \times Aa\)

\[ \begin{aligned} P(AA) &= \frac{1}{4} \\ P(Aa) &= \frac{1}{2} \\ P(aa) &= \frac{1}{4} \end{aligned} \]

Therefore: P(affected) = \(P(aa) = \frac{1}{4}\) P(carrier) = \(P(Aa) = \frac{1}{2}\) P(unaffected) = \(P(AA)+P(Aa)=\frac{3}{4}\)

X-linked recessive example

Mother carrier, father unaffected: \(X^{A}X^{a} \times X^{A}Y\)

\[ \begin{aligned} P(\text{affected son}) &= P(\text{mother passes }X^{a}) = \frac{1}{2} \\ P(\text{affected daughter}) &= P(X^{a}\text{ from mother})\cdot P(X^{a}\text{ from father}) = \frac{1}{2}\cdot 0 = 0 \\ P(\text{carrier daughter}) &= \frac{1}{2} \end{aligned} \]

The key idea is that sons and daughters can have different risks under X-linked inheritance.

How the calculator uses “unknown carrier” probability

Sometimes a parent is listed as “unaffected (unknown).” In that case, the calculator asks for a user-supplied value like \(P(\text{carrier})=\frac{1}{2}\). This creates a genotype mixture:

\[ P(\text{parent genotype}) = \begin{cases} AA & \text{with probability } 1-c \\ Aa & \text{with probability } c \end{cases} \quad\text{where } c = P(\text{carrier}) \]

This is not the same as a population genetics estimate; it is simply a controlled input so you can explore scenarios.

Interpretation tips and limitations

Small families can look consistent with multiple patterns.
Missing people (unrecorded siblings, unknown parents) reduce the power of the heuristic classifier.
Reduced penetrance or variable expressivity can blur patterns in real data.
This tool assumes a single-gene model for the trait.

Use the suggestion mode for learning and hypothesis generation, then use risk mode once a model is chosen.

Frequently Asked Questions

How do I enter a pedigree in this calculator?

Add family members one at a time with an ID, sex, and affected status, then link each child to a mother and father using their IDs. You can also upload a CSV with columns id,sex,affected,mother,father to load a full family quickly.

What does the Suggest pattern mode actually do?

It applies rule-based checks to the entered pedigree (such as generation skipping, male bias, or male-to-male transmission) and ranks the inheritance models. It is a hint for learning and hypothesis generation, not a definitive diagnosis.

Why does Compute risk show different results for sons and daughters in X-linked models?

Sons inherit their X chromosome from the mother and a Y from the father, while daughters inherit one X from each parent. Because the transmission differs by sex, X-linked recessive and X-linked dominant risks can be different for sons versus daughters.

What does P(carrier) mean when a parent is listed as unaffected (unknown)?

It is a user-supplied probability that an unaffected parent is still a carrier (for example Aa in an autosomal recessive model). The calculator uses this value as a genotype mixture to compute the child’s affected and carrier probabilities.

Which inheritance models are supported in this pedigree tool?

The tool supports autosomal dominant, autosomal recessive, X-linked recessive, and X-linked dominant models. Risk calculations follow clean single-gene assumptions with complete dominance where applicable.

Pedigree

Pedigree toolkit

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Family members

Mother (female)

Father (male)

Legend

Calculation steps

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Frequently Asked Questions