prophase I - DNA coils and becomes visible under light microscopes
- sister chromatid cohesion - pairing of homologous pairs side by side
- guided by heterochromatin sequences
- homologues attach to nuclear envelope at specific sites
- recombination nodules - has enzymes for breaking/joining homologous chromatids
- crossing over between sister chromatids is suppressed
- only about 2-3 crossovers per chromosome per meiosis
- sister chromatids held together at centromeres, homologous chromosomal pairs held together where crossing over took place
- chiasma - X-shaped structure where crossover took place
- ensures that the microtubule spindle only attaches to 1 side of centromere
- indicates that crossing over has taken place
metaphase I - nuclear envelope dissolves
- microtubules form spindle like in mitosis
- terminal chiasmata - state of chiasmata where they reach the ends of the chromosomes
- kinetochores only connect to centromeres on 1 side
- chromosome pairs line up on metaphase plate randomly
anaphase I - microtubules begin to shorten
- chiasmata gets broken, homologues get pulled apart
- sister chromatids aren’t split up
- independent assortment - poles can have mixes of maternal/paternal homologues
telophase I - chromosomes located in clusters at each pole
- nuclear membrane reforms around chromosomes, each w/ 2 sister chromatids
- sister chromatids no longer identical due to crossing over
meiosis II - occurs after a brief interphase after meiosis I
- prophase II - nuclear membrane breaks down, microtubule spindle forms
- metaphase II - spindle fibers bind to both sides of centromeres
- anaphase II - sister chromatids split, go to opposite poles
- telophase II - nuclear envelope re-forms
- meiosis I/II result in 4 distinct cells w/ haploid chromosomal set
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