  We calculate the probability distribution of repetitions of ancestors in a
genealogical tree for simple neutral models of a closed population with sexual
reproduction and non-overlapping generations. Each ancestor at generation g in
the past has a weight w which is (up to a normalization) the number of times
this ancestor appears in the genealogical tree of an individual at present. The
distribution P_g(w) of these weights reaches a stationary shape P_\infty(w) for
large g, i.e. for a large number of generations back in the past. For small w,
P_\infty(w) is a power law with a non-trivial exponent which can be computed
exactly using a standard procedure of the renormalization group approach. Some
extensions of the model are discussed and the effect of these variants on the
shape of P_\infty(w) are analysed.
