cell divisions mitosis and meiosis. mitosis division of the nucleus of all cells except sex cells...
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Cell Divisions
Mitosis and Meiosis
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Mitosis
• Division of the nucleus of all cells except sex cells
• Produces 2 daughter cells each with the same amount and type of genetic material as the parent cell
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Synthesis• Also called Interphase of the cell cycle
• Not technically part of Mitosis
• DNA is replicated (copied) to make an exact copy of itself
• Each “new” strand is 1/2 of the “old” strand and 1/2 of newly formed strand
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Prophase
• 1st stage of Mitosis
• Nuclear membrane begins to weaken
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Prophase• Centrioles (Protein structures) form and move to the poles of the nucleus
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Metaphase• Chromosomes line up in the middle
• Spindle fibers extend from the centrioles to the centromeres
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Anaphase• Spindle fibers shorten
• Chromosomes are pulled apart at the centromere
• Chromatids move to the opposite sides
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Telophase• Nuclear membranes begin to reform
• Spindle fibers are gone
• Centrioles begin to disassemble
• Cleavage forms– Cleavage - an indentation in tissue
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Cytokinesis• Nuclear membrane complete
• New cell membrane forms at cleavage
• Exact copy of the original cell
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Cell Division for Sex Cells
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Meiosis
• Division of the nucleus of sex cells
• Produces 4 daughter cells each with the 1/2 amount and type of genetic material as the parent cell
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Meiosis
• The first 1/2 is identical to Mitosis
• Before the 2nd 1/2 the DNA is NOT replicated
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Prophase 1 of Meiosis
• Nuclear membrane begins to dissolve
• Centrioles begin to form and move to the poles
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Metaphase 1 of Meiosis
• Chromosomes line up in the middle
• Spindle fibers extend from the centrioles to the centromeres
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Anaphase 1 of Meiosis
• Spindle fibers shorten
• Chromosomes are pulled apart at the centromere
• Chromatids move to the opposite sides
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Telophase 1 of Meiosis
• Nuclear membranes begin to reform
• Spindle fibers are gone
• Centrioles begin to disassemble
• Cleavage forms
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Cytokinesis 1 of Meiosis
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• Nuclear membrane complete
• New cell membrane forms at cleavage
• Exact copy of the original cell
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Metaphase 2 of Meiosis
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• Single copy of the chromosomes line up in the middle
• Spindle fibers extend from the centrioles to the centromeres
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Anaphase 2 of Meiosis
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• Spindle fibers shorten
• Single Chromosome is pulled apart at the centromere
• Chromatids move to the opposite sides
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Telophase 2 of Meiosis
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• Nuclear membranes begin to reform
• Spindle fibers are gone
• Centrioles begin to disassemble
• Cleavage forms on 4 new cells
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Cytokinesis 2 of Meiosis• Nuclear
membranes complete
• New cell membranes form at cleavage
• 4 cells each with 1/2 the genetic information of the parent cell
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Mutations
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Mutations
• Mutation:– Any change in the sequence (order) of the DNA
• 3 main types– Insertion– Deletion– Substitution
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Results of Mutations
• Benign - not good/not bad– This type of mutation leads to variations of traits•Different hair color, skin color, etc
• Helpful– This type of mutation is beneficial to the organism
• Harmful– This type of mutation interferes with normal protein production and often leads to illness or death
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Variation
• A change in a trait which is caused by a change in the DNA
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Insertion Mutation• If the DNA were a sentence like:
My sister is Betty
Insertion would add 1 or more letters to the sentence:
My sisters is Betty
Bad grammar, but the sentence still makes sense
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Deletion Mutation• Using the same sentence:• My sister is Betty
• Deletion mutation removes one or more letters
• My sister is Btty
• This can still makes sense, but changes the meaning of the sentence which in a cell could change the protein
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Problems with Insertion and Deletion Mutations• Once the message is carried out of the nucleus by RNA (we have not talked about this) all messages are read in 3 base segments
• Adding or removing 1 base causes these segments to be completely changed
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Insertion and Deletion Continued
• Using our sentence the 3 base sequences would look like this:
• MYS IST ERI SBE TTY• Insertion would cause this:• MYS IST ERS ISB ETT Y • Deletion would cause this:• MYS IST ERI BTT Y
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Substitution Mutation
• Still using the same sentence:
• My sister is pretty
• Substitution changes one or more letters
• My mister is pretty
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