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Meiosis

Why do children look different from their parents? Meiosis is the process that allows this to happen. It creates more genetic range and reduces the amount of genetic material in the cell by half.  Sexual reproduction allows each parent to contribute to the child’s genetics.

An image showing the cell division in Meiosis.

In this illustration we see 1 parent cell. We end up with 4 unique daughter cells that have half of the genetic information

This video explains the entire process:
This process occurs in two steps:
 
In meiosis I  the number of chromosomes in the cell goes from 46 to 23. In meiosis II the sister chromatids separate. These are the two strands that makeup chromosomes.
 

Meiosis I

This is the first step of meiosis where the amount of DNA in the cell lowers. Before this, chromosomes replicate, forming two identical sister chromatids. 

Prophase I:

We all have one copy of genes from each of our parents. These pairs of genes exist in chromosome pairs, called homologous chromosomes. In prophase I, homologous chromosomes pair up. Then these chromosomes exchange bits and pieces of DNA in a process called crossing over. Crossing over makes the sister chromatids of the chromosome different in meiosis, instead of identical.

Like mitosis, the chromosomes in this stage cluster and the nuclear envelope disappears. The mitotic spindle, which is the “highway” of the cell, forms. 

Metaphase I:

After crossing over, each of these pairs line up at the center of the cells in a row.  

Anaphase I: 

Chromosomes of the homologous pair get pulled to opposite sides of the cell.

Telophase I:

The nuclear envelope disappears. Each of the two daughter cells now has half of the amount of DNA it had before! 

An image showing the comparison between the processes of Mitosis and Meiosis

Meiosis is like mitosis, except everything happens twice and some switching of genetic material happens.

Meiosis II

After the first set of stages, each daughter cell has one chromosome. Each chromosome has two unique sister chromatids. The purpose of meiosis II is to separate these sister chromatids. 

Prophase II: 

Prophase II occurs in the same was as prophase 1, except this time no crossing over occurs. 

Metaphase II:

Individual chromosomes line up at the center of the cell.

Anaphase II:

Each sister chromatid pulls apart to opposite ends of the cell. 

Telophase II:

The original cell has now formed four unique daughter cells. They each have 23 chromosomes instead of 46!

An image showing the process of Meiosis from 1 parent cell to 4 daughter cells.

In this illustration of meiosis we see 1 parent cell. We end up with 4 unique daughter cells that have half of the genetic information

 
In humans, the only cells that go through meiosis are the sperm and egg cells. This means that these cells have 23 chromosomes, while all the other cells in our body have 46. When the egg and the sperm come together, they form a complete set of 46 chromosomes! Animals can pass along and combine their genes in this process as well. It is an important part of sexual reproduction. 

Other Great Resources

https://www.yourgenome.org/facts/what-is-meiosis

Written by: Pallavi Krishnarao