Science & NatureSexual Reproduction: The Fertilization Process
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This flow chart will explain the fertilization process for both males and females, and how the union of the sperm of the egg occurs. The original version of this selector was created by Meljohn

The Male Fertilization Process
Starting with intercourse
The Female Fertilization Process
Starting with intercourse

Arousal to faciliate entrance to the female's vagina
Insertion of aroused penis into the female's vagina
The male's sperm ejaculates into the female's vagina
Upon encountering the ovum, the sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg

Muscle contractions in the epididymis, prostate and seminal vesicles propel semen from the penis into the woman's vagina. The sperm ejaculated by the male meets the female's egg
Ejaculation during copulation
The vagina and cervix do their part to encourage the sperm, emitting chemical signals that show the path
The sperm head disconnects from its flagellum and the egg travels down the Fallopian tube to reach the uterus

Sperm produces enzymes which allow it to burrow through the outer jelly coat of the egg
The sperm and egg go through cortical reaction where the contents surrounding the egg swell, pushing the other sperm far away from the egg, ensuring that only one sperm fertilizes the egg
If the egg is fertilized, the egg quickly finishes the maturation process, combines with the sperm, and starts dividing rapidly. It continues on to the uterus, and sometime between 6 and 12 days after ovulation it will implant into the thickened lining in the wall of the uterus and pregnancy begins.
Cortical reaction ensures that only one sperm fertilizes the egg. The fertilized egg is called a zygote
The pronucleus from the egg merges with the nucleus from the sperm. Once the two pronuclei merge, cell division begins immediately

This pronucleus forms into the father's future son or daughter!!
The depolarization caused by sperm penetration results in one last round of division in the egg's nucleus, forming a pronucleus containing only one set of genetic information
If the egg is not fertilized, the unfertilized egg will still continue its journey through the fallopian tube and into the uterus, but it will not implant into the uterine wall and the female does not become pregnant.
Approximately four days after fertilization, the zygote has about 100 cells and is called a blastocyst
The dividing zygote gets pushed along the Fallopian tube


The implanted blastocyst continues developing in the uterus for nine months and the female's uterus grows. The implanted blastocyst forms into the mother's future son or daughter!!
When the blastocyst reaches the uterine lining, it floats for about two days and finally implants itself in the uterine wall around six days after fertilization, signaling the beginning of pregnancy