The horse phenotype is assumed to be a consequence of a single gene with an autosomal recessive transmission.

Olympus, Bayesian posteriors and genetic counseling

Pegasus Arion Chiron genealogy

Centaurus (or Chiron) and two nephews of Zeus (Areion and Pegasus) were born in the form of a horse from consanguineous unions. If we assume that the horse phenotype is an autosomal recessive genetic trait, what is the risk of recurrence for Zeys and Demeter?

The computation of genetic risk in the highly endogamous family of an ancient greek god and goddess has been published in this journal (Annales de génétique, Ropartz, 1985) as a pleasant puzzle. This calculation was assumed to be direct and straightforward. However, a Bayesian computation taking in account most of the available information of the risk is possible. Four solutions of this quiz are given. These solutions illustrate the different strategies which can be followed when facing actual genetic problems.

The horse phenotype is assumed to be a consequence of a single gene with an autosomal recessive transmission (Arion is a talking horse son of Poseidon and Demeter). This is however not a realistic hypothesis for an isolated endogamous population living on the top of mount Olympus. Numerous consanguineous matings show that genetic counseling was inefficient.

Calculations (soon to be added, this page is about a bayesian puzzle; this page is not about Greek gods and goddesses mythology.

The existence of a descendant with an human appearance is an element of information which affects the risk estimation of Zeus and Demeter.

Marc Jeanpierre
Who's who on Mount Olympus: Bayesian solutions
Ann. Genet., 1990, 33, 185-189.