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Single-Cell Embryo

1 hour

Source: Centro Riproduzione Assistita, Catania, Italy.

Note:

The two pronuclei—one male and one female—each contain the DNA from one parent that will join to form the unique genetic makeup of a new individual. The imminent mingling of the parents' DNA is the final step of fertilization.

Note:

The zona pellucida performs several vital roles in the reproductive process. Following the entrance of a single spermatozoon, it undergoes a reaction called the "zona reaction" rendering the wall of the oocyte/zygote impermeable to penetration by additional spermatozoa.

Label Key:

  • 1. perivitelline space
  • 2. zona pellucida
  • 3. cell membrane
  • 4. male and female pronuclei
  • 5. polar body

All ages referenced to fertilization, not last menstrual period.
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