Pedigree Probability Calculator

Model pedigree outcomes for common inheritance patterns. Explore genotype probabilities, penetrance, expected counts, and risks. Visualize inheritance paths using tables, exports, charts, and guidance.

Biology Tool

Estimate affected, carrier, and non-carrier outcomes for autosomal and X-linked pedigrees. Use penetrance, child count, and sex distribution for richer family risk planning.

Calculator inputs

Inheritance model

Father genotype

Mother genotype

Male child probability (%)

Penetrance (%)

Planned children

Exact affected target

Use uppercase A as the unaffected allele and lowercase a as the disease allele. For X-linked models, XA is the unaffected allele and Xa is the disease allele.

Formula used

Single child genotype probability: Multiply the parental gamete probabilities from a Punnett-style cross. Sum matching outcomes to get each genotype risk.

Observed affected phenotype: Affected phenotype probability = affected genotype probability × penetrance.

At least one affected child: 1 − (1 − p)ⁿ, where p is the affected phenotype probability and n is the number of children.

Exactly k affected children: C(n, k) × p^k × (1 − p)^n−k.

Expected affected children: n × p.

How to use this calculator

Select the inheritance model that matches the pedigree.
Choose the father and mother genotypes for that model.
Enter the male child probability when sex distribution matters.
Set penetrance if the trait does not always express.
Enter the number of children and the exact affected target.
Submit the form to view summary metrics, genotype tables, and the chart.
Use the export buttons to save the result set as CSV or PDF.

Example data table

Scenario	Inheritance model	Father genotype	Mother genotype	Observed affected risk
Carrier parents	Autosomal recessive	Aa	Aa	25.00%
One heterozygous affected parent	Autosomal dominant	Aa	AA	50.00%
Carrier mother	X-linked recessive	XAY	XAXa	25.00%
Affected father	X-linked dominant	XaY	XAXA	50.00%

Frequently asked questions

1. What does this calculator estimate?

It estimates genotype and phenotype probabilities for one child and for multiple children. It also reports carrier risk, expected affected count, and binomial family outcomes.

2. Why is penetrance included?

Some disease genotypes do not always produce the observed trait. Penetrance lets you convert genetic risk into expected phenotype risk more realistically.

3. When does male child probability matter most?

It matters most for X-linked models because sons and daughters inherit sex chromosomes differently. Autosomal models are not changed by sex distribution.

4. Does carrier probability always mean unaffected?

No. In autosomal recessive cases, carriers are usually unaffected. In dominant models, one mutant copy can already be affected, so the table labels heterozygous risk separately.

5. Can this replace pedigree chart interpretation?

No. It supports pedigree analysis but depends on correct inheritance assumptions and genotype assignments. Real clinical genetics also considers testing, history, and uncertain penetrance.

6. What does exactly k affected children mean?

It uses a binomial model to estimate the probability that exactly your selected number of children are affected out of the total planned children.

7. Why do X-linked tables show male and female results separately?

X-linked inheritance produces different genotype paths for sons and daughters. Separate tables make those conditional risks visible before they are combined overall.

8. What are the genotype symbols used here?

A and XA represent unaffected alleles. a and Xa represent disease alleles. Y indicates the paternal Y chromosome in male offspring.