Carnegie Stage 1c - DREM Database

IN VITRO STAGE 1c SPECIMENS (click here to view all figures)

The stage 1c embryo is called the syngamic embryo or zygote and is the last phase of fertilization. It is sometimes called a founder cell because it gives rise to embryonic stem cells. Stage 1c occurs about 20 hours after in vitro insemination but is elusive since it exists for only a brief period. The pronuclei quickly disappear when their envelopes break down (Figs. 1, 2, 5). Groups of chromosomes that were in the pronuclei assume positions in pairs on the rapidly formed first cleavage spindle thereby bringing about syngamy and the establishment of the integrated genome of the embryo. The chromosomes lie in an agranular zone in the central cytoplasm. Since a nuclear envelope does not form, a nucleus is not present at this substage.

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