Confocal analysis also showed that the ureteric bud tips [16] of Pygo1/Pygo2 null kidneys were dilated and misshaped compared with those of littermates with at least one wild-type Pygo2 allele (Figure 3). In addition, the Pygo1/Pygo2 double-homozygous mutant kidneys also had a decrease of approximately 25% in the number of ureteric bud tips per area compared with littermates with at least one wild-type copy of Pygo2 (Table 2). No significant difference in ureteric bud-tip density was seen between Pygo2+/- and Pygo2+/+ embryos (P = 0.33).