Meiosis Meiosis o A process of reduction division

Meiosis

Meiosis o A process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. n Diploid – 2 sets of chromosomes n Haploid – 1 set of chromosomes n Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

Meiosis o Meiosis usually involves 2 distinct stages n Meiosis II

Prophase I o Part of this phase is similar to mitosis. n The doubled chromosomes coil up and become visible. n The nuclear membrane and nucleolus disappear. n The spindle fibers form Here is how Prophase I is different from prophase in mitosis. o In prophase I, doubled homologous chromosomes group together to form a tetrad. o Thus a tetrad is defined as the grouping of doubled homologous chromosomes. o (Tetra means four. You can see there are four sister chromatids in a tetrad. ) n In mitosis, the doubled chromosomes all remain independent of one another.

o In this picture, the chromosomes that are the same size are homologous. The red are inherited from mom while the blue came from dad. You can see the doubled homologs forming a tetrad. Crossing over is occurring between the sister chromatids on the inside of the tetrad.

Prophase 1 o Crossing over n members of the tetrad swap DNA. Think about this. n Because of crossing over, the four gamete cells produced at the end of meiosis will all be different from one another.

Metaphase 1 o the tetrads will line up in the middle of the cell.

Anaphase 1 o the tetrad splits in half and each doubled chromosome moves away to opposite sides of the cell.

Telophase 1/Cytokinesis 1 o each set of homologous chromosomes have been separated into two daughter cells and the cytoplasm has been divided.

Interphase II o Some cells will skip interphase II. o There is no S because the chromosomes are only copied during the first interphase.

Prophase II o This occurs just like prophase in mitosis. o The nuclear membrane break down. o Spindle fibers form

Metaphase II o The doubled chromosomes line up in the middle of the cell.

Anaphase II o The doubled chromosomes split and each sister chromatid moves to opposite sides of the cell.

Telophase II/Cytokinesis II o The chromosome uncoil. o The nucleolus and nuclear membrane reform. o The spindle fibers break down.

Result of Meiosis o Meiosis produces four different haploid cells (half the number of chromosomes as the parent) that will become sperm in males and eggs in females. o Notice that each cell has two chromosomes (the parent had four), and all the cells are different.

Mitosis vs Meiosis Mitosis Meiosis Results in 2 Diploid Cells 4 Haploid Cells (2 N) (N) Cells are Genetically Identical Genetically Different Occurs in Somatic (Body) Cells Sex Cells

o https: //www. youtube. com/watch? v=k VMb 4 Js 99 t. A&feature=related