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Lec 07 Inheritance of Sameness.docx

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Biology 1001A

Lecture 07: Inheritance of Sameness Stages of mitosis (and their main characteristics) - Mitosis: splits eukaryotic cells into two genetically identical cells - Prophase: DNA (chromatin) condenses into chromosomes (spindle poles form) - Prometaphase: nuclear envelope dissolves; spindle elongates and attaches to chromosomes - Metaphase: each chromosome is attached to both spindle poles o spindle moves chromosomes to midline, halfway between spindle poles - Anaphase: cohesion holding sister chromatids together dissolves, allowing separation o sister chromatids pulled to opposite sides - Telophase/Cytokinesis: cell membrane pinches inward, forming two cells o nuclear envelope reforms o sister chromatids decondense o each daughter cell has one of each sister chromatid pair! Stage of cell division (given micrograph of dividing cell) Role and mechanism of mitotic spindle - Molecular machine that moves chromosomes during mitosis - Have two spindle poles that move to opposite sides of cell, one for each resulting daughter cells - Made of microtubules that radiate outward from microtubule organizing centres - Spindle microtubules can rapidly grow, shrink, and attach to kinetochores on chromosomes - Cannot pierce through nuclear envelope, so nuclear envelope must be dissolved first - Can only grab chromosome when very end touches the chromosome and only remain attached if the chromosome is attached to both spindle poles o this is why more microtubules per spindle pole to grab chromosomes is more efficient o when chromosomes attached to both spindle poles, each pole pulls at chromosome (tug-of-war fashion) Role of cell cycle check points - Mitosis check point: cells will not proceed into anaphase until all chromosomes are attached to spindle - G1-S check point: cells will not replicate their DNA until DNA is fully repaired - G2-M check point: cell must be ready to condense DNA to continue onto mitosis Changes in amount of DNA throughout cell cycle - Cells in human body have 46 chromosomes - Duplicate to 92 DNA molecules during S phase (before mitosis) - 46 sister chromatids are passed on to each daughter cell (after mitosis) Location of actively cycling cells in multicellular - animals: gametes, bone marrow, injury repair
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