Prophase I: - nuclear membrane dissolves
* centrioles move to poles
* spindle fibres forming
* DNA has been replicated and forms chromosomes made of 2 identical chromatids * Homologous chromosomes line up to form a bivalent, 2 chromosomes or 4 chromatids (TETRAD), this process is called SYNAPSIS * Where chromatids overlap is called a CHIASMATA, and it allows for CROSSING OVER of genetic information between chromosomes Metaphase I: - homologous chromosomes (4 chromatids) line up on the equator Anaphase I: - homologous chromosomes separate and each chromosome (2 chromatids) move towards opposite poles (SEGREGATION) Telophase I: - cytoplasm divides to form 2 new cells with 46 chromosomes each the nuclei may not form
NOTE: the cells are not identical
Interphase II: no doubling of DNA, it is just the time between meiosis I/II
Prophase II: - spindle fibres forming
Metaphase II: - chromosomes (2 chromatids) line up on the equator
Anaphase II: - chromatids separate, each one moves to opposite pole
Telophase II: - nuclear membrane forming
* 4 daughter cells are produced, haploid
* 4 sperm but 1 egg (3 polar bodies)
http://projects.cbe.ab.ca/Diefenbaker/Biology/Bio%20Website%20Final/notes/molecular_genetics/3_stages_meiosis.htm Meiosis I
Meiosis I has two main purposes:
It is the reduction division, so it reduces the number of chromosomes in half, making the daughter cells haploid (when the parent cell was diploid). It is during meiosis I that most of the genetic recombination occurs.
Keep in mind that before meiosis begins at all, the DNA undergoes replication, just like it did before mitosis started. So, when you first see chromosomes in meiosis I, they have sister chromatids, just like in mitosis. It is just that in meiosis I, we will be talking about tetrads becoming visible, lining up, separating, and decondensing (rather than...