Fig. 15. Variable number tandem repeats (VNTRs). Although the restriction fragment length polymorphisms (RFLPs) illustrated in Figure 10 show only two alleles (the gain or loss of a single restriction enzyme site) in most circumstances, VNTRs frequently have many different alleles. Three individuals are illustrated, showing the increased potential for heterozygosity in the population. Each arrow represents a sequence, which is repeated a different number of times. The head to tail arrangement of the repeats is a consequence of the means by which the VNTRs are generated, that is, unequal crossing over. Southern blot analysis with a probe adjacent to, but not including, the repeat shows a pattern of regular size increases when several different genomic DNA samples are compared.