Meiosis

what is meiosis

• a type of reduction division that reduces the chromosome number of the parent cell by half

• each gamete has half the number of chromosomes

• meiosis I: homologous chromosomes separate, reducing 2n to n

• meiosis II: sister chromatids separate, creating 4 genetically unique daughter cells

prophase I

chromosomes condense, become visible

• homologous chromosomes pair up in a process called synapses, forming tetrads

• crossing over occurs (homologous chromosoems exch. genetic material)

• nuclear membrane breaks down, spindle fibers begin to form

Metaphase I:

• Tetrads align at the metaphase plate (the cell's equator).

• Spindle fibers attach to the centromeres of homologous chromosomes.

Anaphase I:

• Homologous chromosomes are pulled apart to opposite poles of the cell by the spindle fibers.

• Sister chromatids remain attached at their centromeres.

Telophase I and Cytokinesis:

• Chromosomes reach the poles of the cell.

• The nuclear membrane may reform temporarily

• The cell divides into two haploid daughter cells, each containing one chromosome from each homologous pair.

prophase II

• Chromosomes condense again if they decondensed after meiosis I.

• The nuclear envelope breaks down, and spindle fibers form in each haploid cell.

Metaphase II

• Chromosomes align individually at the metaphase plate.

• Spindle fibers attach to the centromeres of the sister chromatids.

Anaphase II

• Sister chromatids are separated at the centromeres and pulled to opposite poles of the cell.

• Each chromatid is now considered an individual chromosome.

elophase II and Cytokinesis

• Chromosomes reach the poles of the cells and begin to decondense.

• The nuclear envelope reforms around each set of chromosomes.

• Cytokinesis divides the cells, resulting in four haploid daughter cells, each with a unique combination of chromosomes due to crossing over and independent assortment.