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cell cycle, Chromosomal mutations, Chromosomes identification, Change in…
cell cycle
interphase
S
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After replication, two copies stay joined to each other and are called sister chromatids
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G1
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Signaling molecules can cause cell to accumulate molecular changes during G1 that promote progression through the cell cycle
If the cell passes the restriction point, or G1 checkpoint, the cell becomes committed to enter S phase and replicate DNA
cytokinesis
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In most cases, mitosis is quickly followed by cytokinesis
Meiosis
Meiosis I
Prometaphase I
spindle apparatus complete, chromatids attach to kinetochore microtubules
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Prophase I
chromosomes condense, bivalents form and the nuclear membrane breaks down
Cytokinesis
End of meiosis I – two haploid cells, with no pairs of homologous chromosomes
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Meiosis II
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Sister chromatids separated in anaphase II, unlike anaphase I
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M
mitosis
Metaphase
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When this alignment is complete, the cell is in metaphase
Pairs of sister chromatids are aligned along a plane halfway between the poles called the metaphase plate
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Prometaphase
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Two kinetochores on each pair of sister chromatids are attached to kinetochore microtubules from opposite poles
Telophase
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Kinetochore microtubules shorten, pulling chromosomes toward the pole to which they are attached
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The two poles move away from each other as overlapping polar microtubules lengthen and push against each other
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Decision to divide
Internal factors
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Checkpoints
Cyclins or cyclin-dependent kinases (cdks) responsible for advancing a cell through the phases of the cell cycle
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G2 checkpoint:
Checks for DNA damage, determines if
all of the DNA is replicated, and monitors
the levels of proteins needed for M phase.
G1 checkpoint:
(restriction point) Determines if conditions are
favorable for cell division and if
the DNA is damaged. G1 cyclin is made in response to sufficient nutrients and growth factors.
Metaphase checkpoint:
Determines if all chromosomes are Determines if all chromosomes are attached to the spindle apparatus
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