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Biol 121- 2010.01.25- Genetics- Mitosis, Cytokinesis, Chromosome Structure, Cell Cycle Regulation.docx

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ANTH 100
Paul Hewitt

Biol 121 225 Freeman 227240 Ch 11Jan 25 10 How many chromosomes do 46 chromosomes in each cell human and potato plants have What is the general structure of eukaryotic chromosomes normally exist as extremely long threadlike strands eukaryotic chromosomes consisting of DNA associated with globular proteins called histones in eukaryotes the DNAprotein material is called chromatin Chromatids each ofthe DNA copies in a replicated chromosome is called a chromatidchromatids from the same chromosome are called sister chromatidsthey representexact copies of the same genetic materialeach chromatid contains one long DNA double helix At start of M phase each at the start of M phase each chromosome consists of two sister chromatids that are chromosome attached to each other at the centromereas mitosis begins chromatin condenses to form a much more compact structureduring mitosis the two sister chromatids separate to form independent chromosomes and one copy of each chromosome goes to each of the two daughter cells Prophase first step of mitosis chromosomes and centrosomes have already replicated during interphase during prophase the chromosomes condense into compact structures chromosomes first become visible in light microscope during prophasein cytoplasm prophase is marked by formation of the mitotic spindlea structure that produces mechanical forces that pull chromosomes into the daughter cells during mitosis via depolymerisation the mitotic spindle consists of an array of microtubulescomponents of the cytoskeleton groups of microtubules attach to the chromosome and are called spindle fibres in all eukaryotes spindle fibres originate from a microtubule organizing centerthe nature of which varies among species in animal cells this microtubule organizing center is a centrosomea structure that contains a pair of centrioles during prophase in all eukaryotes the mitotic spindle either begin moving to opposite sides of the cell or form on opposite sides Prometaphase once chromosomes have condensed nucleolus disappears and the nuclear envelope fragments or breaks down after the nuclear envelope has disintegrated spindle fibres from each mitotic spindle attach to one of the two sister chromatids of each chromosome at the kinetochore the kinetochore the attachment between the spindle fibres and each chromatid is made at a structure called the kinetochore kinetochores are located at the centromere region of the chromosome where sister chromatids are attached to each other each chromosome has two kinetochores where spindle fibres attachone on each sideduring prometaphase in animals the centrosomes continue their movement to opposite poles of the cell in all groups the microtubules attached to the kinetochores begin moving the
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