Figure 5.5 Unequal crossing over generates gene families. The left side illustrates an unequal crossing over event and the two products that are generated. One product is deleted and the other is duplicated for the same region. In this example, the duplicated region contains a second complete copy of a single gene (B). The right side illustrates a second round of unequal crossing over that can occur in a genome that is homozygous of the original duplicated chromosome. In this case, the crossover event has occurred between the two copies of the original gene. Only the duplicated product generated by this event is shown. Over time, the three copies of the B gene can diverge into three distinct functional units (B1, B2, and B3) of a gene family cluster.