Single-Cell Embryo

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