Meiosis1

• Meiosis I is the reductional cell division, the chromosomes number is reduced by half (from 46 to 23 chromosomes)
• meiosis II is the equational cell division similar to mitosis which maintains the chromosomes number of organism (maintain 23 chromosome).
• prophase, I, the chromosomes have already duplicated.
• Leptonema where replicated chromosomes have coiled and are already visible. The number of chromosomes present is the same at the number in the diploid cell.
• zygonema, the homologous chromosomes begin to pair and twist each other in highly specific manner. Homologous chromosomes are identical in terms of visible structures
• The pairing is called synapsis
• because the pair consist of four chromatids it is referred to as bivalent.
• pachynema, chromosome become much shorter and thicker
• A form of process of physical exchange of a chromosome region is called crossing-over.
• diplonema, where two pairs of sister chromatids begin to separate from each other.
• It is at this point where crossing-over is shown to have taken place and the area of contact between two non-sister chromatids, called chiasma,
• diakinesis, where the four chromatids of each tetrad are even more condensed and the chiasma often terminalize or move down the chromatids to the ends.
• metaphase I, the centrioles are at opposite poles of the cell.
• Anaphase I begins when the two chromosomes of each bivalent (tetrad) separate and start moving toward opposite poles of the cell as a result of the action of the spindle
• telophase I. At this stage homologous chromosome pairs complete their migration to the two poles as a result of the action of the spindle. Now a haploid set of chromosomes is at each pole, with each having two chromatids.