Conception of identical twins

Millions of sperm are released during a single ejaculation. Their tails propel on their journey to encounter the single egg cell. Of the millions of sperm, only a few will survive to reach the egg and just one will penetrate the egg cell’s wall to combine it’s genetic material with that of the egg in the process called fertilization. If during the first week of cell division, the fertilized egg cell, or zygote, divides into 2 zygotes, identical twins will form. Each developing embryo contains the same genetic material as the other.

Conception of identical twins

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Review Date: 11/12/2021

Reviewed By: John D. Jacobson, MD, Department of Obstetrics and Gynecology, Loma Linda University School of Medicine, Loma Linda, CA. Also reviewed by David Zieve, MD, MHA, Medical Director, Brenda Conaway, Editorial Director, and the A.D.A.M. Editorial team.

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