Cell Divisions

Mitosis and Meiosis

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

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

Prophase

• 1st stage of Mitosis

• Nuclear membrane begins to weaken

Prophase• Centrioles (Protein structures) form and move to the poles of the nucleus

Metaphase• Chromosomes line up in the middle

• Spindle fibers extend from the centrioles to the centromeres

Anaphase• Spindle fibers shorten

• Chromosomes are pulled apart at the centromere

• Chromatids move to the opposite sides

Telophase• Nuclear membranes begin to reform

• Spindle fibers are gone

• Centrioles begin to disassemble

• Cleavage forms– Cleavage - an indentation in tissue

Cytokinesis• Nuclear membrane complete

• New cell membrane forms at cleavage

• Exact copy of the original cell

Cell Division for Sex Cells

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

Meiosis

• The first 1/2 is identical to Mitosis

• Before the 2nd 1/2 the DNA is NOT replicated

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

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

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

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

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

Mutations

• Mutation:– Any change in the sequence (order) of the DNA

• 3 main types– Insertion– Deletion– Substitution

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

Variation

• A change in a trait which is caused by a change in the DNA

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

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

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

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

Substitution Mutation

• Still using the same sentence:

• My sister is pretty

• Substitution changes one or more letters

• My mister is pretty