Identification of the homozygous recessive genotype for the deficiency of uridine monophosphate synthase in 35-day bovine embryos.

Holstein-Friesian cattle heterozygous for the deficiency of uridine monophosphate (UMP) synthase have half-normal activity of UMP synthase. The homozygous recessive genotype would result in little or no activity, has not been observed among live animals and apparently leads to embryonic mortality at approximately Day 40 of gestation. Activity of UMP synthase averaged 2.74 +/- 0.61 units/mg protein for 19 obligatory normal embryos (from normal x normal matings). Activity for 18 embryos from heterozygote x heterozygote matings yielded three non-overlapping groups as follows: (i) five presumed normals with greater than two-thirds normal activity, (ii) ten apparent heterozygotes with one-third to two-thirds normal activity and (iii) three putative homozygous recessive embryos with less than one-third normal activity. The distribution among these groups was consistent with the 1:2:1 ratio expected for autosomal inheritance. Conception of embryos homozygous recessive for this disorder was demonstrated.