Slideshow: Early Events
Single-Cell Embryo
#40, Slide 3 of 24
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. |
