Model for the expansion of the ZNF gene cluster in 19p12. A hypothetical model is proposed in which the pericentromeric region of 19p12 is in a state of expansion and contraction owing to saltatory amplification and/or unequal crossing-over of β-satellite repeats in this region. A functional ZNF progenitor gene associates with β-satellite repeats in 19p12 ∼50 mya. The region continues to expand and contract, effectively carrying the inserted ZNF gene as part of its heteromorphism. Expansion becomes favored over contraction among the β-satellites owing to the placement of a functional gene within its context that confers a selective advantage. This leads to the formation of a large cluster of tandemly duplicated ZNF genes in the anthropoid ancestor.