Embryonic lethality in

Sca-1^−/−;W^v/W^vcompound homozygotes. (A) The ratio of wild-type,W^v/+, andW^v/W^v pups fromW^v/+ heterozygous intercrosses. A total of 178 pups were genotyped from 4 breeding pairs. HomozygousW^v/W^v pups were born at a slightly lower-than-expected, but not statistically significant, Mendelian ratio for a nonlethal mutation (P > .1). (B) The ratio of Sca-1^−/−, W^v/+;Sca-1^−/−, andW^v/W^v;Sca-1^−/−pups from W^v/+;Sca-1^−/−heterozygous intercrosses. A total of 288 pups were genotyped from 9 breeding pairs. Compound homozygousW^v/W^v;Sca-1^−/−pups were observed at an 84% reduction compared withW^v/W^v pups fromW^v/+ heterozygous intercrosses, demonstrating that mostSca-1^−/−;W^v/W^vcompound homozygotes die in utero (P < .0001).