Meiosis

Topics: Mitosis, Chromosome, Meiosis Pages: 2 (261 words) Published: January 21, 2014
Interphase

Prophase I
Early Prophase I
D.N.A coils tightly and individual chromosomes become visible as single structures Homologous chromosomes become associated in synapsis. Each pair of chromosome is called a bivalent. Centrioles divide and move to the opposite poles of the cell, and spindles start to form

Late Prophase I
The bivalents duplicate to form tetrads (four-chromatid groups).The nuclear membrane disintegrates. Chromosomes join at points called chiasmata where crossing over takes place.

Metaphase I
The nuclear membrane completely disappears. Spindle fibres attach to the chromosome’s centromeres and homologous pairs move together and line up along the metaphase plate.

Anaphase I
Spindle fibres pull homologous chromosomes towards opposite poles of the cell. This separates the chromosomes into two haploid set.

Telophase I
The homologous chromosomes arrive at there specific opposite poles. The cell membrane begins to constrict and a cleavage is formed. The nuclear envelope reforms around the daughter nuclei.

MEIOSOS II
Prophase II
This marks the beginning of the second meiotic division, two new cells are not completely formed. The nuclear envelope disintegrates, centrioles begin to move to opposite poles of the cell and spindle fibres start to appear. Metaphase II

Spindle is fully formed and chromosomes line up separately at the equator of the cell due to the spindle fibres. Anaphase II
The centromeres divide and the spindle fibres pull the chromatids to opposite poles of the cell Telophase II
Four daughter cells are now formed. The chromosomes uncoil, lengthen and become very indistinct. The spindle fibres disappear and the nuclear envelope re-form around each nucleus.
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