Meiosis Sex cell reproduction..

Meiosis The process of reproduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Meiosis only occurs in our gametes (sex cells). The results of meiosis are haploid cells. Diploid - two sets; both sets of chromosomes - both the mother and the father’s chromosomes - represented by 2N

What are Diploid Cells? Diploid - two sets; both sets of chromosomes - both the mother and the father’s chromosomes - represented by 2N Human somatic (body) cells are diploid, meaning there is a total number of 46 chromosomes (23 pairs) in these cells.

What are Haploid Cells? Haploid - one set; just one set of chromosomes - from either the mother or the father - represented by N -Human gametes (sex cells) are haploid, meaning they have a total number of 23 chromosomes.

2 parts of Meiosis Meiosis is broken down into 2 parts: Meiosis I and Meiosis II Meiosis I is exactly the same process as mitosis, with the exception of crossing-over (which takes place in prophase I)

Crossing-Over Where chromosomes pair up to form tetrads(4 arms) and exchange portions of their chromatids. - this results in the exchange of alleles between homologous chromosomes to produce new combinations of alleles - happens during Prophase I

Meiosis 1: It’s steps are exactly the same as mitosis.

Meiosis II Meiosis I has now created 2 new cells after cytokinesis. Now.. Each of these cells will undergo another round of division. Meiosis II, remember 2 cells are dividing now. The end result will be 4 genetically different cells. - each will only have 1 set chromosomes, making them haploid.

Meiosis II cont… In males, after meiosis II takes place, 4 sperm cells are produced. In females, after meiosis II takes place, 1 egg and 3 polar bodies are produced. Polar bodies will not develop into offspring.

Meiosis II Prophase II - centrioles separate - spindle fibers begin to form

Meiosis II Metaphase II - chromosomes in each cell line up in the middle of the cell - chromosomes attach to spindle fibers at the centromere

Meiosis II Anaphase II - each chromosome breaks apart and forms a chromatid - chromatid migrate to poles of the cell

Meiosis II Telophase II - chromatid gather at poles and lose their shape - nuclear membrane begins to reappear - spindle fibers disappear

Cytokinesis The two cells undergo cytokinesis shortly after telophase II and the end result is 4 genetically different cells. Each cell is haploid

The Whole Picture

The End