Table 2. Het x Het crosses of initial floxed Poldip2 mice fail to produce homozygotes.

	Observed counts		Observed total	Expected total
genotype	male	female		1:2:1	1:3
WT	13	11	24	30.75	30.75
Het	49	50	99	61.50	92.25
Hom	0	0	0	30.75
Total	62	61	123	123	123

Pups were genotyped by conventional PCR. Both methods described in Fig 2 produced identical results. All breeders were known to be heterozygous because one of their parents was a wild type. No homozygote pup was identified and there was no difference between male and female counts. Observed pup genotype counts were significantly different from the expected 1:2:1 Mendelian distribution (P = 10⁻⁴), but not from a 1:3 distribution (P = 0.18).