Cell Division(Mitosis)The cell division cycle is a series of events that take place in a cell leading to its division and duplication. In unicellular species such as bacteria, cell division occurs by a process called binary fission and produces a new organism. In multicellular species a somatic cell (body cell) division occurs. These are: Interphase Interphase consists of 3 phases; G1 phase (growth), S phase (replication) and G2 phase (preparation for division). During interphase, cells prepare for mitosis mainly by gathering nutrients and conducting normal cellular functions. G1 phase G1 phase, protein synthesis occurs and the cell grows to about double its original size. More organelles are produced, increasing the volume of the cytoplasm. S phase During S phase, DNA is replicated to produce exactly two identical chromosomes. At the end of S phase, all of the chromosomes have been replicated. G2 phase Cell undergoes necessary cell growth and production of microtubules required for mitosis. Mitosis Mitosis consists of prophase, metaphase, anaphase and telophase. The pairs of chromosomes condense and attach to fibres that pull the sister chromatids to opposite sides of the cell. In a standard mammalian cell, mitosis can typically take around 1 hour to complete. The cell then divides in cytokinesis, to produce two identical daughter cells. Prophase The chromatin slowly condense to chromosomes. Each chromosome has duplicated during the preceding S phase and consists of two sister chromatids. Towards the end of prophase, the cytoplasmic microtubules disassemble and the mitotic spindle begins to form. Metaphase Metaphase, proteins called kinetochores attach to some of the spindle microtubules, which are called kinetochore microtubules. These are responsible for aligning the chromosomes in one plane between the poles of the cell. This is called the metaphase plate. Anaphase Begins as the chromosomes are pulled to opposite ends of cell, slowly start to separate. Telophase New nuclear envelope re-forms around each group of chromosomes CytoKinesis The cytoplasm then divides in a process called cytokinesis. The membrane is drawn inward to form a cleavage burrow, leaving two separate daughter cells. And the cycle starts again!!!!! Meiosis I and 2 The process of Meiosis is the same as Mitosis except there are 2 divisions but only occur in sex cells. 1) Interphase : The number of chromosomes, which is 46 (or 23 pairs), duplicates and the cell prepares for division.
2) Prophase 1: Each chromosome begins to condense and pair together with its homologue, or matching chromosome. Homies cross, each give a part. 3) Metaphase 1: Proteins attached to microtubules move the spindle poles apart and the chromosomes line up in position in the middle of the cell. 4) Anaphase 1: Microtubules from the spindle poles begin to lengthen and pull each chromosome away from its homologous partner. The separated chromosomes begin moving to the poles, with each homolog moving to opposite ends. 5) Telophase 1: The cytoplasm divides and now we have two cells, each with 46 chromosomes. 6) Prophase 2: Microtubules attach to the chromosomes and proteins drive the movement of these chromosomes towards the equator of the cell. 7) Metaphase 2: In each daughter cell, all the chromosomes are now lined up at the spindle equator in the middle of the cell. 8) Anaphase 2: The sister chromosomes break and each sister moves to opposite ends of the cell, towards each pole. 9) Telophase 2: Now each cell divides in half. Since we had two cells dividing, we now have 4 cells. Each of these 4 cells contains only 23 chromosomes since there was no Interphase 2. Mens Vs Women, The Battle of the Genesis
Gametogenesis is the formation of gametes. The formation of eggs is oogenesis and the formation of sperm is spermatogenesis.
Spermatogenesis The cell that undergoes meiosis is a primary spermatocyte. The first meiotic division produces two secondary spermatocytes and the second division producesspermatids, which mature to form sperm. Meiosis I, Meiosis II, and the maturation process each take approximately 16 days (48 days total). Males do not run out of sperm because mitosis precedes each meiosis. Human males produce approximately1000 sperm per second (30 billion/year). Each ejaculation should contain 200 - 300 million sperm. Oogenesis Oogenesis occurs in the ovary. Each of the divisions in humans is unequal. During the first meiotic division, a large secondary oocyte and a small polar body are produced. The secondary oocyte will divide to produce an egg and a polar body. The first polar body may divide to produce two more polar bodies. Although the polar bodies are very small and nonfunctional, they contain a full set of chromosomes. Meiosis in human females begins before person is born but stops in prophase I and does not resume until after puberty. Each month secondary oocytes are released at ovulation. The second meiotic division resumes after penetration by sperm. In humans, secondary oocytes are fertilized. Eggs are produced only after fertilization of a secondary oocyte. Women are born with all of the primary oocytes that they will ever have (2 million). Yeast LabYeast was a great example as they can reproduce through meiosis. When there's plenty of food, yeast cells reproduce themselves to take advantage of it. Most yeast put out a small bud from one side of themselves, and move a piece of their nuclei into it, and then they gradually pinch off the bud to make a new, smaller yeast cell. Yeast can also reproduce in a more complicated way throughmeiosis.
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