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Slide 1

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· There are 46 chromosomes in most of your body
· Chromosomes are found in the nucleus of a cell.
· Before a cell divides by mitosis, it duplicates its
· Mitosis is where a cell splits to create two
genetically identical copies.
· Mitosis produces new cells to replace those which
are damaged.
· We need mitosis to grow.…read more

Slide 2

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Cell Division Process - Mitosis
"Mitosis is when a cell reproduces itself by splitting to form two
identical offspring"
· In a cell that's not dividing, the DNA is all spread out in long strings.
· If the cell gets a signal to divide, it needs to duplicate its DNA ­ so
there's one copy for each new cell. The DNA is copied and forms X-
shaped chromosomes. Each `arm' of the chromosomes is an exact
duplicate of the other.
· The chromosomes then line up at the centre of the cell and cell
fibres pull them apart. The two arms of each chromosome go to
opposite ends of the cell.
· Membranes form around each of the sets of chromosomes. These
become the nuclei of the two new cells.
· Lastly, the cytoplasm divides.
· You now have two new cells containing exactly the same DNA ­
they're identical.…read more

Slide 3

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Some organisms use
mitosis to reproduce. For
example, strawberry
plants produce runners
this way, which become
new plants. This is known
as asexual reproduction.
The offspring have exactly
the same genes as the
parents, which means
there's no genetic
variation.…read more

Slide 4

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· Meiosis takes place in the gametes.
· Gametes are sex cells that only have one copy of
each chromosome.
· Gametes have half the usual number of
chromosomes so that when two gametes join
together during fertilisation the resulting fertilised
egg will have the full number of chromosomes.
· When the chromosomes are first pulled apart in
meiosis, it creates a random mixture (assortment)
of the father's and the mother's chromosomes, so
each new cell is unique.…read more

Slide 5

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Cell Division Process - Meiosis
"Meiosis produces cells which have half the normal number of
· As with mitosis, before the cell starts to divide, it duplicates
its DNA to produce an exact copy.
· For the first meiotic division the chromosomes line up in their
pairs across the centre of the cell.
· The pairs are pulled apart, mixing up the mother's and
father's chromosomes into the new cells. This creates
genetic variation.
· The chromosomes line up across the centre of the nucleus
ready for the second division, and the left and right arms are
pulled apart.
· There are now 4 gametes, each containing half the original
number of chromosomes.…read more


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