Educational Pedigree Genotype Probability Calculator

Relationships make the probability calculation joint

For every compatible assignment of AA, Aa and aa to the entered members, the calculator multiplies founder prior probabilities and Mendelian transmission probabilities. Evidence excludes incompatible assignments. Summing the remaining weights and normalizing gives a posterior distribution for each member.

An offspring can inform the parents, which in turn changes the distribution for another offspring. Treating each person's evidence independently would discard that shared structure. This implementation enumerates the bounded configuration space directly, up to 3¹⁰ assignments, using scaled log weights for small probabilities.

The founder assumption is a visible input

P(AA)=(1−q)²; P(Aa)=2q(1−q); P(aa)=q²

Each unrelated founder starts with the same user-entered a-allele frequency and Hardy–Weinberg prior. A known genotype then conditions that prior. Boundary q values can make some entered evidence impossible; the calculator reports the contradiction rather than inventing a posterior.

A_ means the exact set {AA, Aa} under complete dominance and full penetrance. It is not a clinical unaffected category. The probability of the evidence measures its weight in the stated model and does not measure whether the pedigree is true.

Posterior uncertainty must stay visible

A dominant-class offspring of Aa × Aa is not equally likely to be AA or Aa. The original weights are 1/4 and 1/2; excluding aa and dividing by 3/4 yields 1/3 and 2/3. The result keeps all three probabilities for every member.

The same listed ancestor may contribute through more than one relationship path, because each member is represented once in the joint model. Founders are assumed unrelated. Missing parents must be represented explicitly as distinct unknown founders rather than silently supplying a population average.