  We consider a (sub) critical Galton-Watson process with neutral mutations
(infinite alleles model), and decompose the entire population into clusters of
individuals carrying the same allele. We specify the law of this allelic
partition in terms of the distribution of the number of clone-children and the
number of mutant-children of a typical individual. The approach combines an
extension of Harris representation of Galton-Watson processes and a version of
the ballot theorem. Some limit theorems related to the distribution of the
allelic partition are also given.
