Meiosis Lesson for Kids: Definition & Stages

Instructor: Fedora Sutton Butler
Learn about the generation of sex cells, or gametes, by the process known as meiosis. See how the four phases - prophase, metaphase, anaphase and telophase - differ between meiosis I and II.

Cells

Animals and plants are made up of cells, and these cells contain special compartments. One of these compartments is called a nucleus. What is inside the nucleus? The structures carrying the cell's genes. What are these structures called? Chromosomes.

Did you know that there are many different types of cells? For example, some cells contain two sets of chromosomes, while others contain only one set of chromosomes.

Somatic cells, or body cells in humans contain 46 chromosomes, or two sets of 23 chromosomes.

Gametes, or sex cells contain only one set of chromosomes. In humans, gametes each contain 23 chromosomes.

Meiosis is the process of producing gametes. The process occurs in two steps, meiosis I and meiosis II.

We'll start with the first step, meiosis I. This is the step during which the two sets of chromosomes are reduced to only one set in each cell.

Meiosis I

Let's see how meiosis I works in a somatic cell that comes from a hamster which has 44 chromosomes.

To make things simple, we will follow four of these chromosomes. Our image shows two blue chromosomes from the male parent and two red chromosomes from the female parent.

In prophase I, we can start to see the chromosomes as they begin to separate and the membrane around the nucleus begins to disappear.

Then in metaphase I, identical chromosomes, one from the male and one from the female, are arranged in the middle of the cell and fibers are attached to move the chromosomes to each end of the cell.

Preparation for separation of chromosomes and cell division
Prophase I and Metaphase I

Now that the chromosomes are in the middle of the cell, is this a good time for the cell to divide?

Nope, not yet. First the chromosomes must move to either end of the cell.

Now we're in anaphase I, when the fibers shorten and move the chromosome to which it is attached to each side of the cell. Now the cell is ready to divide into two.

chromosomes separate cell divides and nucleus reforms
Anaphase I and Telophase I

This happens in telophase I. During this phase, the fibers disappear, the cell divides into two and the nucleus reforms in each cell.

So how many chromosomes out of the starting 4 chromosomes are found in each cell at this point? Two! (Notice there has been a reduction in the number of chromosomes by one half.)

If we were looking at all the starting chromosomes in the hamster's cell, how many would there be? Answer = 44. Since we get a reduction by one half as a result of meiosis I, then how many chromosomes would be present in each cell at the end of meiosis I? Answer = 22.

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