What inheritance patterns does the tool support?

It supports autosomal recessive, autosomal dominant, and X-linked recessive inheritance.

What do the parent probability fields mean?

Their meaning depends on the selected mode: carrier probability for recessive models and affected probability for the dominant model.

What does the autosomal recessive calculation return?

It returns the probabilities of an affected child, a carrier child, and an unaffected non-carrier child.

How does the X-linked recessive model report results?

It reports overall affected-child probability plus separate affected-son, affected-daughter, and carrier-daughter probabilities.

Can this replace genetic counseling?

No. The calculator is for educational use and does not replace professional genetic counseling or medical advice.

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Pedigree Probability Tree — Offspring Disease Risk

Step-by-step Mendelian probability tree for pedigree problems: autosomal recessive P(affected) = carrier × carrier / 4, autosomal dominant both-affected 3/4, X-linked recessive carrier mother → 50% affected sons. Derived from Griffiths, Hartl & Clark 2007, StatPearls. Educational use only.

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2 examples

Two cystic fibrosis carriers: 1/4 affected, 1/2 carriers

Classic autosomal recessive pedigree: both parents are known carriers (Aa) of cystic fibrosis — the tree multiplies P(father transmits a) = 1 × 1/2 by P(mother transmits a) = 1 × 1/2, giving P(affected child aa) = 1/4 = 0.25. The carrier branches sum to 1/2 and the homozygous-normal branch is 1/4, so every pregnancy has a 25% chance of being affected — the textbook 1:2:1 genotype ratio.

{"result":"Autosomal recessive: P(affected child) = 0.25, P(carrier) = 0.5, P(unaffected non-carrier) = 0.25.","metadata":{"input":{"inheritanceMode":"autosomal-recessive","fatherProbability":1,"motherProbability":1},"result":{"mode":"autosomal-recessive","affectedChild":0.25,"carrierChild":0.5,"unaffectedChild":0.25}}}

Hemophilia: carrier mother × unaffected father

X-linked recessive pedigree (hemophilia A): an obligate-carrier mother (X^A X^a, probability 1) and an unaffected father (X^A Y, probability 0). The son branch gives P(affected son) = 1 × 1/2 = 0.5; the daughter branch gives P(affected daughter) = 0. Averaged over a 1:1 sex ratio, P(affected child) = 0.25 and P(carrier daughter) = 0.5 — the crisscross pattern where affected men pass the allele to carrier daughters, never to sons.

{"result":"X-linked recessive: P(affected child) = 0.25 (sons 0.5, daughters 0), P(carrier daughter) = 0.5.","metadata":{"input":{"inheritanceMode":"x-linked-recessive","fatherProbability":0,"motherProbability":1},"result":{"mode":"x-linked-recessive","affectedChild":0.25,"affectedSon":0.5,"affectedDaughter":0,"carrierDaughter":0.5}}}

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4 options

SettingsAdjust formats, ranges, numbers, and modes.4

Inheritance ModeselectRequiredAutosomal recessive: probabilities are carrier probabilities. Autosomal dominant: probabilities of being affected (heterozygous). X-linked recessive: father = probability affected, mother = probability carrier.Father Carrier/Affected ProbabilitynumberRequiredRecessive: P(father is a carrier). Dominant: P(father is affected, heterozygous Aa). X-linked recessive: P(father is affected).Mother Carrier/Affected ProbabilitynumberRequiredRecessive: P(mother is a carrier). Dominant: P(mother is affected, heterozygous Aa). X-linked recessive: P(mother is a carrier).Decimal PlacesnumberOptional

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Pedigree Probability Tree — Offspring Disease Risk

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1. Two cystic fibrosis carriers

2. Hemophilia risk from a carrier mother

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3. Autosomal dominant pedigree exercise