Stages of mitosis and meiosis

AS level Biology A OCR spec

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  • Created on: 31-10-16 14:48
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The main stages of mitosis:
BEFORE mitosis occurs: during interphase all the DNA in the nucleus is replicated, each DNA
molecule is converted into identical DNA molecules called chromatids The 2 chromatids are joined
together at the centromere ­ it is essential that they are kept together during mitosis so that they
can be segregated correctly (1 into each new daughter cell)
During interphase DNA combines with proteins called histones to form a dense complex called
chromatin
Cytokinesis: this process usually begins in anaphase and ends in telophase, but is separate to
mitosis.
In animals: a cleavage furrow forms around the middle of the cell and the cell-surface membrane is
pulled inwards by the cytoskeleton until it is close enough to fuse around the middle producing 2
new daughter cells that are genetically identical.
2.1.6 Cell division, cell diversity and cellular organisation

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In plants: plants have cell walls so it's not possible for a cleavage furrow to form. Instead vesicles
assemble in the same place as the spindle equator was formed. The vesicles fuse with each other
and the cell surface membrane dividing the cell into 2. Then new cell wall is created along the new
sections of membrane.
The main stages of meiosis:
· There are 2 divisions in meiosis: meiosis 1 and meiosis 2. After interphase the cells enter
meiosis 1:
2.1.…read more

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Meiosis 2: the 2 daughter cells now undergo: prophase 2, metaphase 2, anaphase 2, telophase 2
and cytokinesis in the same way as meiosis 1 except with half the number of chromosomes.
In anaphase 2: the sister chromatids are separated with each new daughter cell inheriting 1
chromatid from each chromosome. 4 haploid daughter cells are produced.
2.1.…read more

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