Meiosis

=MEIOSIS = =[|Source of the picture]=

ANIMATION [] ** SOURCE: ** Sadava, et al., //Life: The Science of Biology,// Ninth Edition, Sinauer Associates © 2010 Sinauer Associates, W. H. Freeman & Co., and Sumanas, Inc.

MEIOSIS OVERVIEW

What is Meiosis? Meiosis is the type of cell division in haploid cells. When haploid cells divide they produce genetically different gametes. This means that every haploid cell, egg or sperm, is genetically different. The DNA of the gametes gets exchanged in the various steps of meiosis.

STEPS OF MEIOSIS

The real first step of meiosis one, the first process of cell division, is called interphase. When a cell is not in the process of dividing the cell will be in interphase which is the time the cell needs to grow and carry out it's normal functions.

The first step of meiosis is prophase 1. During prophase 1 the homologous chromosomes pair up and form a tetrad. The tetrads then exchange their DNA in a form known as crossing over. Crossing over is when the DNA from the homologous chromosomes becomes mixed. Prophase is shown in number one of the picture shown above. A closer look of crossing over can be shown in the picture below. [|Source of picture]

The second step of meiosis is metaphase 1. During metaphase 1 the chromosomes line up in the middle of the cell and the spindle fibers will attach themselves to the chromosomes. In metaphase 1 the process of independent assortment will occur. Independent assortment is when the DNA from the chromosomes becomes scrambles and randomly put together when being lined up on the spindle fibers. As shown as number two in the main picture above. A closer look of independent assortment can be found in the image below. [|Source of picture]

The third step of meiosis is anaphase 1. Anaphase 1 is when the spindle fibers pull the chromosomes apart. They end up on opposite sides of the cell. This is shown in number three in the main image above.

The fourth step is teleophase 1 and cytokinesis. This is when the nuclear envelope forms again and the cell divides into two separate haploid cells, that are not genetically the same. This is shown in step four in the main image.

Now that there are two genetically different haploid cells, meiosis two will begin in order to produce more cells.

Prophase 2 is the fifth step in meiosis. Prophase 2 is when the number of chromosomes in the cell splits in half. This is shown in number five on the main picture.

Metaphase 2 is the sixth step of meiosis. As shown in number six on the main picture the chromosomes will again line up in the middle of the cell and the spindle fibers will attach themselves to them.

The seventh step of meiosis is anaphase 2. During anaphase 2 the sister chromatids will divide and move to opposite sides of the cell. The is shown in step 7 on the main picture above.

The final step of meiosis is telophase 2 and cytokinesis. This process is when the two cells divide yet again and produce four haploid cells. This process is shown in step eight on the main image.

MISTAKES OF MEIOSIS

Sometimes there are mutations that can happen when the cell does the process of meiosis. The chromosome mutations are changes in the structure of a chromosome or the loss or gain of a chromosome. There are four different types of chromosome mutations.

Deletion- this is when a piece of a chromosome is broken during division and lost.

Duplication- is when a piece of a chromosome is copied and appears twice on a chromosome.

Inversion- is when a piece of a chromosome breaks during division and reattaches in different places on the same chromosome.

Translocation- is when a piece of a chromosome breaks during division and reattaches to a different chromosome.

VIEWING CHROMOSOMES

In order to view what is happening inside the chromosome scientists use the process of karyotyping. Karyotyping is a snapshot of the chromosomes that allows us to count how many chromosomes we have.

DISORDERS

Down Syndrome is a disorder that can result when an extra chromosome is present.

Jacob's Syndrome is a normal male with an extra Y chromosome.

Klinefelter Syndrome is a male with an extra X chromosome. This makes the male very tall and infertile.

Turner Syndrome is a female with only one X chromosome. This makes the female short and infertile.

(all facts on this wiki were from the textbook or the worksheets that were given to us during class.)