DETECTION OF THE HOMOZYGOUS RECESSIVE GENOTYPE FOR DEFICIENCY OF URIDINE MONOPHOSPHATE SYNTHASE BY DNA TYPING AMONG BOVINE EMBRYOS PRODUCEDIN-VITRO

A PCR-based DNA test for the genetic defect resulting in the deficienc y of uridine monophosphate synthase (DUMPS) was developed for embryoni c cells to identify the homozygous recessive genotype. This genotype i s usually lethal at about day 40 of gestation. Oocytes from a cow, het erozygous for DUMPS, were fertilized in vitro with spermatozoa from a DUMPS-carrier bull and cultured in vitro until the morula or blastocys t stage. Embryos were matured in vitro, fertilized and cultured accord ing to a method established in our laboratory. Heminested PCR was perf ormed and the genotype of twelve embryos were unambiguously determined by the AvaI digestion of the PCR products. Among these embryos two in dividuals homozygous for the defective DUMPS allele (R405 --> STOP) we re detected. From the remaining ten embryos, four were homozygous and six were heterozygous for the normal allele. The observed distribution is close to the expected ratio of 1:2:1. These results further suppor t the monogenic recessive inheritance of the defect.