Chiasma Frequency and Disjunctional Behavior of Ewe and Cow Oocytes Matured In Vitro

Abstract

Oocytes obtained from adult female sheep and cattle were studied during in vitro meiotic maturation for cytogenetic data. Ninety-three diakinesis/first-metaphase ewe preparations obtained afer 16–24 hr of culture had an average chiasma frequency per bivalent of 1.30. One hundred and seventy-seven ewe second-metaphase ova obtained at 23–48 hr of culture contained 27 symmetrical chromosomes. One possible heterozygote was seen at second metaphase, but was not reflected in appropriate first-metaphase configurations. One hundred and nine diakinesis/first-metaphase cow preparations obtained after 8–26 hr of culture had an average chiasma frequency per bivalent of 1.19. Ninety-nine cow second-metaphase ova obtained at 19–48 hr of culture contained 30 chromosomes plus 3 which were diploid. Comparisons with in vivo findings for these species and in vitro data for other species are made.