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For an organism to grow, rebuild tissues, and reproduce, cells must divide. Every division requires replicating and then evenly dividing the cell’s massive jumble of DNA. This video segment follows the stages of mitosis, the systematic process that ensures that daughter cells formed when plant and animal cells divide get equal shares of DNA.

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Mitosis: The Amazing Cell Process that Uses Division to Multiply! (Updated)

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Read pages 321-322

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Read pages 16-21 only

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Only Slides 1-9!

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When there are many differences and variations in a species it helps to keep that species healthy.

Meiosis is a process that allows an improved range of genetics because it only contains half of a cell's genetic material so that the other half can be contributed by another source.

Meiosis is part of sexual reproduction and each parent can give their half to their offspring.

The process of meiosis is very complex, but it narrows down to two main steps:

Meiosis I reduces the number of chromosomes from the original 46 down to 23.

Meiosis II there is a separation of the sister chromatids and the results are two strands.

Here are the details of how our cells accomplish meiosis:

4 Phases of Meiosis I

This is the phase involving the reduction of the amount of DNA.

Prophase I:

All of us have one copy of our genes that we got from each of our parents. These pairs or sets are chromosome pairs and go by the name of "homologous chromosomes."

There is a "pairing up" of the homologous chromosomes in prophase I and this is also where they exchange DNA pieces in a "crossover" process.

It's different in meiosis, as the crossing over creates different chromosome chromatids; not like mitosis, which makes them identical.

Meiosis and mitosis do have actions that are similar in this stage as the chromosomes cluster, there is a disappearance of the nuclear envelope, and there is a formation of the cell "highway" called the mitotic spindle.

Metaphase I

Once the crossing over process is complete the pairs will go to the center of the cell and line up in a row.

Anaphase I

Those homologous chromosome pairs are each pulled to the opposing cell sides.

Telophase I

This is where the nuclear envelope completely vanishes and if you see the two daughter cells you will note that they now have only half of their previous DNA.

4 phases of Meiosis II

After meiosis I, there is one chromosome in each of the daughter cells, and each of those chromosomes have two sister chromatids that are unique. The goal of meiosis is in the separation of these sister chromatids.

Prophase II

Prophase II happens during the same time period as prophase I, with the exception that there isn't any crossing over.

Metaphase II

This is the lining up in the cell center of the individual chromosomes.

Anaphase II

The sister chromatid will pull apart so that each is at the cell's opposite ends.

Telophase II

From the original cell we have seen the process complete so that it has now formed four unique daughter cells that have 23 chromosomes instead of the original 46.

The only human cells that go through meiosis are the egg and sperm cells. Each parent contributes 23 chromosomes so that the species has a healthy diversity. All other cells in our bodies have 46 chromosomes.

Interesting Facts about Meiosis

The process of meiosis must be absolutely perfect from start to finish. Lacking or extra chromosomes, or misalignment can result in an abnormal outcome. Down Syndrome (Trisomy 21) is an example of the 21st chromosomes failing to separate properly and adding an extra chromosome.

The chromosomes and DNA that we get from each parent is completely different, but some DNA is considered to be "dominant" while others are "recessive". This is why so many of the family members may have brown hair and brown eyes or even olive skin. Those are the dominant genes in our chromosomes.

The body cells of a species have a basic basic number of chromosomes and it's called the somatic number and is labelled 2n.

Meiosis is important because it keeps the chromosome numbers from doubling each generation.

Bacteria don't use meiosis to reproduce. Instead, they use a process called binary fission.

Just before the crossing over process starts, there is a pairing up of both of the homologous chromosomes to form a structure that is called a "tetrad."

Interesting Facts about Biology

Scientists have classified living things into five kingdoms. However viruses aren't included in any of these kingdoms, so they aren't bacteria, protists, plants, fungi, or animals.

A majority of viruses are so incredibly small that they can't be seen even with an optical microscope.

Seaweed isn't a plant. Instead it's a kind of algae that is found in the ocean.

In an average human body, carbohydrates make up between 2-3% of the total mass.

Your spine is made up of 33 bones.

The bone marrow that creates red blood cells makes around 5 billion per day.

Meiosis Quiz

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Meiosis Facts for Kids (All You Need to Know!)

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When there are many differences and variations in a species it helps to keep that species healthy. Meiosis is a process that allows an improved range of genetics because it only contains half of a cell's genetic material so that the other half can be contributed by another source.