Sex Cells

Contributor: Hannah Brooks. Lesson ID: 12631

How do we come to look like we look, and not all look alike? How does a baby know how to become a boy or girl? Microscopic instructions contained in cells combine to make you you and not someone else!


Life Science

learning style
personality style
Grade Level
Middle School (6-8)
Lesson Type
Dig Deeper

Lesson Plan - Get It!


Why do all humans have the same parts but look so different? Why do we sort-of look like our family members?

You may look similar to your siblings or cousins, but you have unique features that make you, you!

This occurs because you are a blend of the genetic material from each of your parents. That genetic material, or DNA, is stored in every cell in your body. Somatic cells, or body cells, hold 23 pairs of DNA organized in chromosomes.

Somatic cells include each type of cell we have studied in this series, Human Body Cells. If you missed or would like to review the previous lessons, find them under Related Lessons in the right-hand sidebar.

Humans also have sex cells that hold half the number of chromosomes. Sex cells also hold sex chromosomes. Females have XX chromosomes, while males have XY chromosomes. These sex chromosomes pass on important genetic material to offspring. Sex cells are ovum, or eggs, found in females, and sperm, found in males.

Human eggs are much larger than sperm. They are round and are produced in the ovaries during the process of oogenesis. Oogenesis, or egg development, occurs when the cell divides unequally during cell division processes in meiosis. Meiosis is the process where one cell divides into four cells with half the genetic material. During this process, one egg and three polar bodies are formed. Polar bodies are smaller cells that do not mature. Egg cells carry one X chromosome to contribute to the offspring. This process occurs before the female infant is born, and the eggs reach maturation during puberty, triggered by the production of sex hormones.

Females are born with a limited number of eggs held in the ovary, ready to be released one-at-a-time for ovulation during the menstrual cycle.

Male sex cells are called "sperm." Sperm are motile, meaning that they can move on their own. They use a flagellum, or a tail, to swim. Sperm cells also have a head region that is made of proteins designed to penetrate an ovum during sexual fertilization. Sperm are produced during spermatogenesis. It is a process very similar to ovum development, but results in four equal-sized sperm cells. Males produce millions of sperm each month, that are stored in the testes.

Sperm can either carry an X or an Y chromosome, determining the sex of offspring from sexual fertilization.

Sex cells are a critical part of human reproduction. They ensure that genetic information is passed from parents to offspring, but allow for a blend, so that we are not clones of our parents! Females have large ovum that are produced during oogenesis and stored in the ovary, while males use spermatogenesis to produce millions of sperm.

Each sex cell has a unique structure: eggs are round, and sperm can move independently.

  • Why do you think it is important for sex cells to contain half the genetic information of a body cell?
  • How might a sperm's structure influence the function?

Discuss these questions with a parent or teacher.

In the Got It? section of the lesson, you will learn more about scientific vocabulary associated with sex cells.

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