Meiosis

MEIOSIS 1 PROPHASE 1

● CHROMOSOMES WERE DUPLICATED EARLIER IN INTERPHASE ● THEY START TO CONDENSE ● EACH PAIRS WITH ITS HOMOLOGUE AND SWAPS SEGMENTS ● NEW MICROTUBULES ARE FORMING A BIPOLAR SPINDLE ● ONE OF THE TWO CENTROSOMES MOVES TO THE OPPOSITE SIDE OF THE NUCLEAR ENVELOPE WHICH BEGINS TO BREAK UP

MEIOSIS I METAPHASE I

● ONE SET OF MICROTUBULES HAS TETHERED ONE CHROMOSOME OF EACH TYPE TO ONE SPINDLE POLE AND ANOTHER SET TETHERED ITS HOMOLOGUE TO THE OTHER SPINDLE POLE ● A TUG OF WAR OF SORTS HAS ALIGNED THE CHROMOSOMES MIDWAY BETWEEN THE TWO SPINDLE POLES

MEIOSIS I ANAPHASE I

● ONE OF EACH DUPLICATED CHROMOSOME, MATERNAL OR PATERNAL MOVES TO A SPINDLE POLE ● ITS HOMOLOGUE MOVES TO THE OPPOSITE POLE ● MOTOR PROTEINS AND MICROTUBULES ALLOW FOR THIS MOVEMENT

MEIOSIS I TELOPHASE I

● ONE OF EACH TYPE OF CHROMOSOME HAS ARRIVED AT THE SPINDLE POLE ● IN MOST SPECIES, THE CYTOPLASM DIVIDES AT THIS TIME ● ALL OF THE CHROMOSOMES ARE STILL DUPLICATED

MEIOSIS II PROPHASE II

● IN EACH CELL ONE OF THE TWO CENTRIOLES MOVES TO THE OPPOSITE SIDE OF THE CELL AND A NEW BIPOLAR SPINDLE FORMS ● SOME SPINDLE MICROTUBULES HARNESS ONE CHROMATID OF EACH CHROMOSOME TO A SPINDLE POLE ● OTHER MICROTUBULES HARNESS ITS SISTER CHROMATID TO THE OTHER POLE

MEIOSIS II METAPHASE II

● BY NOW MICROTUBULES FROM BOTH SPINDLE POLES HAVE FINISHED A TUG OF WAR ● THEY HAVE ALIGNED ALL OF THE STILL DUPLICATED CHROMOSOMES MIDWAY BETWEEN THE POLES

MEIOSIS II ANAPHASE II

● THE SISTER CHROMATIDS OF EACH CHROMOSOMES MOVE APART AND ARE NOW INDIVIDUAL UNDUPLICATED CHROMOSOMES ● MICROTUBULES PULL THEM TOWARD OPPOSITE SPINDLE POLES AS OTHER MICROTUBULES PUSH THE POLES APART ● A PARCEL OF ONE OF EACH TYPE OF CHROMOSOME WILL END UP NEAR EACH POLE

MEIOSIS II TELOPHASE II

● A NEW NUCLEAR ENVELOPE ENCLOSES EACH PARCEL OF CHROMOSOMES SO THERE ARE NOW FOUR NUCLEI ● THE CYTOPLASM DIVIDES ● EACH OF THE DAUGHTER CELLS NOW HAS A HAPLOID (N) OF UNDUPLICATED CHROMOSOMES

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