TABLE 1.

Mthfd1 null mice are not viable

Mthfd1^gt/+ mice were intercrossed and their progeny genotyped. The expected genotype distribution was calculated based on a Mendelian distribution. Differences between observed and expected genotype and sex distributions were analyzed by Chi square analysis. p values ≤ 0.05 were considered significantly different.

Genotype	Observed genotype distribution			Expected genotype distribution
	Male	Female	Total	Male	Female	Total
Mthfd1+/+	15	24	39	17.5	17.5	35
Mthfd1gt/+	46	54	100	34.5	34.5	69
Mthfd1gt/-	0	0	0	17.5	17.5	35
Total	61	78	139	69.5	69.5	139
Number of litters observed					26
Mean litter size (mean ± S.E.)					5.3 ± 0.4
p value, observed versus expected genotype distribution (1:2:1)					2.7 × 10-11
p value, observed versus expected genotype distribution assuming homozygous lethality (1:2:0)					nsa
p value, observed versus expected sex distribution					ns

^ans, not significant.