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Meiosis
What is Meiosis?
Another type of cell
division
 Production of
gametes

• Sperm
• Eggs
Chromosome Number
 Homologous
– one chromosome
from each parent
 A cell that has both sets of
homologous chromosomes is diploid
(2n) – where ‘n’ is the number of
different chromosomes
 A cell that contains only one of each
chromosome is haploid (n)
Chromosome Number cont.
 Gametes
are haploid…
 If the sperm or egg were diploid, the
zygote (fertilized egg) would have
too many chromosomes
• 46 + 46 = 92
 Because
the sperm or egg are
haploid, the zygote has the correct #
• 23 + 23 = 46
Phases of Meiosis

Meiosis involves
two divisions in
which the
chromosome
number will be cut
in half
• Meiosis I
• Meiosis II
Meiosis I
Synapsis – the
pairing of the
homologues


Interphase I – cells
make copies of the DNA
Prophase I – each
chromosome pairs with
the corresponding
homologue forming a
tetrad (4 chromatids)
• Crossing-over may
occur, where portions
of the chromatids are
exchanged
Meiosis I cont.
 Metaphase
I – the homologous pairs
line up at the equator
 Anaphase I – one homologue from
each pair goes to each pole
 Telophase I & Cytokinesis – nuclear
membranes form & the cell divides
into two cells
Meiosis II
 No
Interphase between Meiosis I &
Meiosis II
 Meiosis II is essentially identical to
Mitosis (except at the end there will
be 4 haploid daughter cells)
Males vs. Females
In males, the
gametes that are
formed are the
sperm
 4 sperm are
produced per
parent cell

In females, the
gametes that are
formed are the
eggs
 1 egg is produced
per parent cell
 Each division of the
cell is uneven

Males vs. Females cont.
Mitosis vs. Meiosis
Mitosis
Meiosis
Type of Cell
Regular body
cells
Sex cells only
# of divisions
1
2
# of daughter
cells
2
4
Diploid
(identical to
parent)
Growth &
repair
Haploid
(different from
parent)
diploid/
haploid
purpose
reproduction
Fun Meiosis Facts!
 The
egg cell is the largest cell
humans produce!
 Sperm cells are the smallest cells
produced by humans!
 Human Females are born with all of
the eggs they will have in there
lifetime.
 Males will continue to make sperm
cells throughout their life.
THE END!!!