biology 1406

• Somatic cells (nonreproductive cells) have two sets of chromosomes
• Gametes (reproductive cells: sperm and eggs) have half as many chromosomes as somatic cells
• Gametes are produced by a variation of cell division called meiosis which is a special type of mitosis that yields nonidentical daughter cells that have only one set of chromosomes
The cell cycle consists of:
• Interphase (G1,S,G2) phase. (cell growth and copying of chromosomes in preparation for cell division). the cell grows in all phases, but chromosomes are only duplicated in the S phase.
• Mitotic (M) phase: (mitosis and cytokinesis) after the comesomes are duplicated, the mitotic phase splits them into tow cells:
• Mitosis: hapenes in 5 stages:
1)Prophase : where the mitotic spindles start to form and the nuclear envelope starts to disapear
2)Prometaphase: the mitotic spindles attach to the knetochore of the sister cromatids.
3)Metaphase: the mitotic spindles pull the cromosomes to the midle of the cell, making a line.
4)Anaphase: the mitotic spindles split the sister cromosomes to the oposit ends of the cell.
5)Telaphase: identical nucli form at each end of the cell, and cytokinesis starts.
• Cytokinesis: starts during Telaphase and the cell wall devides to make tow identical cells, the mitotic spindals eventually disassemble.
– cleavage furrow (animals: microfilaments squeeze the animal cell until it splits.
-cell plate (plants): a new cell wall is formed in the middle of the cell.• The mitotic spindle is a structure made of microtubules that controls chromosome movement during mitosis by conecting to the kinetacore (centrosomes construct such microtubles)
• centrosomes : are responsible of making the mitotic spindles, replicate during interphase and migrate to opposite sides of the cell in order to have one centrosome pull half the cromosomes to each daughter cell
• Kintochore: they conect to the mitotic spindals, and they move the cromatits by depolymerizing the…

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