Mitosis/Meiosis Notes (copy)

@@Cell@@

• @@The smallest structural and functional unit of an@@ ^^organism.^^
• ^^Somatic cells^^ are any cells other than germ cells.
  • Found throughout the body.
  • %%46%% chromosomes in humans.
• %%Germ cells%% contain half the number (%%23%%) of chromosomes.
  • %%Only found in the reproduction organs. (ex: Ovaries)%%

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Cell Division

There are ^^two^^ types of cell division

1. @@Mitosis in somatic cells results in offspring exactly the same as the parents. Involves one “set” of stages.@@

2. Meiosis in germ cells results in a variety of genetically different offspring. Involves two “sets” of stages. (Meiosis 1 and Meiosis 2)

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Vocabulary

• ^^Chromatid^^ - each of 2 thread-like strands into which a chromosome divides during mitosis.
• Sister chromatids - 2 identical copies of a chromatid.
• %%Centromere%% - a structure in a chromosome that holds the two chromatids together.
• ^^Spindle fibers^^ - control the movement and separation of chromosomes during mitosis.
• %%Centriole%% - helps in the formation of spindle fibers.
• %%Nuclear envelope%% - a membrane that separates the nucleus from the cytoplasm in eukaryotic cells.

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Mitosis

• Used for cell ^^division.^^

• Asexual reproduction

  • Binary fission
  • ^^Budding^^
  • Regeneration
  • Vegetative Reproduction
  • Fragmentation

• Examples: Some types of %%jellyfish%%, worms, and plants.

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%%4%% basic phases.

1. Prophase
2. Metaphase
3. Anaphase
4. Telophase/cytokinesis

Occurs in a strict sequential order called the ^^cell cycle.^^

==Produces== %%diploid%% ==cells (2) - same genetic makeup as the parent cell.==

Prophase

• The first phase of ^^Mitosis.^^
• Chromosomes become ^^visible^^ through a microscope
• spindles begin to form
• Nuclear membrane %%breaks down%%
• The chromosomes replicate and are seen as a pair of chromatids.

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^^Metaphase^^

• Second phase of mitosis
• ^^The chromosomes, guided by the spindle fibers,^^ %%line up%% ^^in the middle of the dividing cell.^^
• The centrosomes are now at opposite ends (^^spindle poles^^) of the cell.

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%%Anaphase%%

• Third phase of mitosis
• the two sister chromatids of each chromosome are ^^pulled apart^^ by the spindle fibers.
• Chromosomes ^^pull away^^ from each other toward the poles.
• ==The cell== %%elongates%% ==so that the poles are farther apart.==

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@@Telophase@@

• The last stage of mitosis
• The chromosomes have %%reached%% the poles.
• Two new nuclear envelopes form around each of the two separated sets of unreplicated chromosomes.
• ==The cell has divided into two== ^^daughter cells^^ ==exactly like the parent cell.==

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^^Interphase^^

• Mitosis is now over.
• %%Chromatin%% is unwound
• ^^Here the cell^^ %%replicates%% ^^its chromosomes in preparation for another round of cell division.^^

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Meiosis

• ==Cell division occurs in 2 sets of stages. Meiosis 1 and Meiosis 2.==
• ^^Reduces^^ the number of chromosomes in the parent cell by half.
• Produces %%4%% gamete cells.

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Vocabulary

%%homozygous chromosomes%% - During meiosis there are %%matching%% paternal and %%matching%% maternal

^^Crossing over - the process where homologous chromosomes pair up and^^ %%exchange genetic material%% ^^to form new chromosomes^^.

haploid cells - ^^four^^ cells as a result of meiosis, which are ^^genetically different^^ from each other and their parent cells.

Meiosis 1 and Prophase 1

• The first phase of Meiosis 1
• Chromosomes become ^^visible^^ under a microscope.
• Duplication of homologous chromosome pair and cross-over occurs.
• The ^^nuclear envelope^^ disappears.
• Spindles enter nucleus

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Meiosis 1 and Metaphase 1

• The crossover is complete.
• Chromosomes move toward the center and ^^line up.^^
• Spindle fibers attach to the ^^centromere^^ of each chromosome.

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Meiosis 1 - Anaphase 1

• Cell starts to lengthen.
• Two c^^hromatid^^s of each chromosome pair separate and move toward opposite poles by the spindle fibers.
• In meiosis the chromatids remain ^^together.^^

Contrast with mitosis, where sister chromatids ^^seperate.^^

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Meiosis 1 - Telophase 1

• Complete haploid (4) sets of chromosmes

• A clevage of furrow appears

• By the end of the stage the parent cell has divided into two %%daughter cells.%%

• This separation of cytoplasm is called ^^cytokinesis.^^

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Interkinesis in Meiosis

• a period of ^^rest,^^ called interkinesis
• No replication of %%DNA%% occurs during this phase.

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^^Meiosis 2 - Prophase 2^^

• first step in Meiosis 2
• ^^Begins with^^ 2 ^^daughter cells from meosis 1.^^
• @@Chromosomes are condensed.@@
• Nuclear envelope begins to break down.
• Centrosomes have replicated and are moving toward the @@poles.@@

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Meiosis 2 - Metaphase 2

• The second step of Meiosis 2
• The spindles draws the chromomes to the @@center plate.@@

The centromeres are bound to the ^^spindle fibers^^ from opposite sides.

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Meiosis 2 - Anaphase 2

• the third step of Meiosis 2
• Very similar to Meiosis 1 anaphase.
• The two sister chromatids of each chromosome are pulled apart by the @@spindle fibers@@.
• Chromosomes move away from each other toward the poles.
• The cell elongates so that the poles are farther @@apart.@@

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^^Meiosis 2 - Telophase 2^^

• Chromosomes reach o%%pposite%% poles.
• Cytokinesis occurs (seperation of cytoplasm) and nuclear envelopes form.
• ^^Meiosis is complete with 4 daugher cells (haploid) each different from each other and different from the parent cell.^^

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Summary of meiosis

From of cell division that results in half the number of chromosomes in %%gametes.%%

Maintains the ^^same^^ number of chromosomes from generation to generation.

^^Results in an^^ @@assortment@@ ^^of genetic material passed on to offspring.^^