Repetitions within a given genealogical tree provide some information about
the degree of consanguineity of a population. They can be analyzed with te
chniques usually employed in statistical physics when dealing with fixed po
int transformations. in particular, we show that the tree features strongly
depend on the fractions of males and females in the population, and also o
n the offspring probability distribution. We check different possibilities,
some of them relevant to human groups, and compare them with simulations.