meiosis biology

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definition

MEIOSIS: DIVISION OF A PARENT CELL THAT PRODUCES

GENETICALLY DIFFERENT HAPLOID CELLS

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stage one

STAGE ONE

each chromosome duplicates to become double stranded (like in mitosis)

each strand is called a chromatid

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stage two

STAGE TWO

each chromosome becomes thicker, shorter and more visible. then chromatids are then joined at the centromere.

the nuclear envelope disappears

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stage three

STAGE THREE

spindle fibres spread out from each end of the cell and attach to the centromere of each chromosome

similar* chromosomes then pair up in the centre of the cell

*the scientific word homologous can be used

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STAGE FOUR

STAGE FOUR

Small parts of the homologous chromosomes cross over

this exchage of genetic material increases variation (eventually creating the different haploid cells)

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stage five

STAGE FIVE

the spindle fibres contract, seperating the homologous pair into opposite sides of the cell, which begins to divide

each chromosome is still formed of two chromatids

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stage six

STAGE SIX

a new nuclear envelope forms around each set of chromosomes and the cell finishes dividing

each cell only has 46 chromosomes

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STAGE SEVEN

STAGE SEVEN

The 2nd part of meiosis begins with the chromosomes condensing again and the nuclear envelopes disapearing

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stage eight

STAGE EIGHT

spindle fibres spread out at right angles and attach to the chromosomes.

the fibres contract, seperating the two chromatids in each chromosome. Each cell divides in two.

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stage NINE

STAGE NINE

a new nuclear envelope forms around each set of chromosomes.

each cell contains 23 chromosomes and each chromosome is genetically different. 

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