When genotypes are used as the genetic states X of a Gibbs sampler, the problem of reducibility of the Markov chain frequently occurs at multiallelic loci. Basically, when we update an individual, the genotype of his neighbors may preclude the transition to some of his potential genotypes. The state space will then be divided in many isolated subsets called islands. The solution proposed by S. Lin is to alternate Gibbs steps with Metropolis steps allowing to jump from one island to another (Lin [6]).