Meiosis- has two parts meiosis 1 and meiosis 2. Meiosis occurs in sperm and eggs. Through many steps the genetic information that the sperm and egg carry is split up and sent to 4 different daughter cells. Each daughter cell has half as many chromosomes as the parent cell. The daughter cells are haploid (n). Prophase 1- The nucleus disappears and the nuclear envelope will breakdown so the chromatin can condense into visible chromosomes as the spindles form. Homologous chromosomes pair up, this process is called synapsis. At this point crossing over of genetic information can occur due to the intertwining of chromatids. Crossing over involves breaks in each pair of chromosomes, they can then recombine with the opposite homologous chromosome.

(Pictures taken from Danton H. O'Day, PhDProfessor of ZoologyCell & Developmental Molecular BiologyUniversity of Toronto at Mississaugawww.erin.utoronto.ca/~w3odaywww.erin.utoronto.ca/~w3bio315www.erin.utoronto.ca/~w3bio380)

Metaphase 1- When the cell has reached this part of the process the cell has already formed the spindle fibers. At the end of the spindle fibers there are microtubules attached to the spindle fibers. At this time the chromosomes come to the middle of the cell, then anaphase occurs.

Pictures taken from Danton H. O'Day, PhDProfessor of ZoologyCell & Developmental Molecular BiologyUniversity of Toronto at Mississaugawww.erin.utoronto.ca/~w3odaywww.erin.utoronto.ca/~w3bio315www.erin.utoronto.ca/~w3bio380

Anaphase 1- After the chromosomes collect at the center of the cell they then are pulled away towards the microtubules. Because the chromosomes are being pulled towards the microtubules the chromosomes then begin to split up.

Telophase 1- During telophase two daughter cells are formed from the set of two homologous chromosomal pairs. At this stage the nuclear wall then begins to reappear.

Prophase 2- During prophase 2 there is a second meiotic division but it is not as complex as prophase 1. The spindle fibers are now reformed.

Metaphase 2- During metaphase 2 the condensed chromosomes line up on the nuclear wall while the centromeres are being attached to the microtubules.

Anaphase 2- During anaphase 2 the chromosomes are split and are attracted to the poles of the cell

Telophase 2- Each of the chromatids is now a chromosome. The daughter cells each contain a haploid genome of 23 chromosomes. Both of the cells are different due to crossing-over.