Carnegie stage 1
Human early zygote showing pronuclei
The early human zygote where the male and female pronuclei (centre of image) have not yet combined to form the single zygote nucleus. These pronuclei contain all the nuclear DNA (genes) and are the nuclei from the sperm and egg.
Two of the egg's polar bodies (right, 3 o'clock position of image) are shown at the edge of the egg cytoplasm. These polar bodies contain the excess DNA from the meiotic divisions of the egg.
The zona pellucida (edge of image) forms a specialised thick extracellular matrix layer around both the egg and the developing conceptus for the first week.
Facts: Week 1, size 0.1-0.15 mm
Cite this page: Hill, M.A. (2020, July 3) Embryology Carnegie stage 1. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Carnegie_stage_1