One Egg - One Sperm

How to give young people the tools they need to know they have a purpose.  

  • Vocabulary: Gonads
    • Many people think that this is slang for testicles, but in fact, it is a medical term that described the part of the female and male anatomy that create and release sex cells.  Gonads = Ovaries & Testicles. 
  • Vocabulary: Gamete
    • Both male & female gonads create gametes.  Male & female gametes are different. The male gamete, or sperm, and the female gamete, the egg or ovum, meet in the female's reproductive system.  The male gamete’s nucleus contains X or Y chromosome. The female gamete’s nucleus contains an X chromosome.

During intercourse, millions of sperm will leave the penis and enter into the vagina.  Some of those sperm will make the journey through the cervix and into the uterus with the hopes of making it to the fallopian tube that has an egg.   

Explaining how this all happens is a little confusing to some young people.  There is an assumption that if you are getting into the nitty-gritty like this you have already explained the internal reproductive anatomy. 

Things to clarify:

  1.  The fallopian tube has adhesive sites that are responsible for egg pickup from the ovaries and movement into the tube. Eggs move slowly through the reproductive organs propelled by gravity and the innate design. 
  2. Sperm can move, swimming like a tadpole; they have a head and tail.  

How they meet:

An egg is released upon maturity from one of the two ovaries and enters the fallopian tube.  

The sperm must swim from the penis into the female reproductive tract. Some sperm will not make it through the cervix, others will not choose the correct fallopian tube.  Some will reach the egg. 

The first sperm to reach the egg that has the correct shape, called morphology, will enter the outer shell of the egg, shedding its tale. Only one sperm can enter the egg.  


Other great resources can be found at your local library. A favorite on these topics is "It's So Amazing!: A Book about Eggs, Sperm, Birth, Babies, and Families" by Robie H. Harris

One Cell + One Cell = Zygote

Once the egg has accepted this single sperm they are now a Zygote.  This zygote builds into more and more cells, a combination of the information provided by the sperm and the egg.

Over the next 3-5 days the zygote moves to the uterus, it will attach to the uterine lining. There it will begin to grow into an embryo.  By 8 weeks, when most people find out that they are pregnant, the embryo is about the size of a jelly bean or kidney bean. If the embryo was viable, meaning healthy, at around 11 weeks, when it is about the size of fig or slightly smaller than a lime it would now be termed a fetus.  From this point forward the fetus grows inside of the uterus.  

Visual explanation for easy understanding: This video is wonderful for parents to understand how fertilization works.  If you are interested in a visual this could be appropriate for some school aged young people. Watch the video and judge what portions may be the most appropriate 2:05 to 2:50 follow the information in the post above.


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