Transcript MEIOSIS

MEIOSIS
Why Meiosis?
• Meiosis is a form of cell division that produces
haploid cells.
• A haploid cell contains one full set of
chromosomes. In human, the haploid cells are
the sex cells – sperm & egg – which contain 23
chromosomes.
• Sex cells = gametes = germ cells.
• A regular body cell is a diploid cell that contains
two full sets of chromosomes – one from mom
and one from dad. The number of chromosomes
in a human diploid cell is 46 (2 x 23).
• Meiosis uses diploid body cells to create the
haploid sex cells and, for this reason, is known
as reduction division.
Meiosis – Same But Different
• Meiosis has some similarities to
mitosis in terms of the actions and
movement of the chromosomes within
the cell.
• The main difference between meiosis
and mitosis is that meiosis has two
rounds of division and creates four
haploid sex cells while mitosis has
only one round of division and gives
way to two identical, diploid, daughter
cells.
The Stages of Meiosis
• The names of the stages of meiosis are
the same as those of mitosis except that
there are two rounds of division so you
must indicate which division (I or II) you
are dealing with.
• This means that you have Prophase I in
the first round of division and Prophase II
in the second.
• Overall…
InterPIMIAITIPIIMIIAIITIIInter
Interphase  Prophase I
• DNA as chromatin.
• Nucleus in place.
• Centrioles present
but not at poles.
• Nucleolus present.
• DNA = chromosomes.
• Chromosomes in groups
of four called tetrads.
• Nucleus dissolving.
• Centrioles migrating to
the poles of the cell.
Metaphase I  Anaphase I
• Centrioles at poles
of cell.
• Spindle formed –
microtubules
attached to tetrads.
• Nucleus gone.
• Tetrads are pulled
apart. (4  2 pairs)
Telophase I  Prophase II
• Chromosomes pairs
are at opposite ends
of cells.
• Cytokinesis takes
place.
• Cytokinesis is
complete.
• Centrioles migrate
to opposite poles.
Metaphase II  Anaphase II
• Chromosome pairs
line up in middle of
cell.
• Centrioles are at
poles of cell and
form the spindle.
• Chromosome pairs
are pulled apart and
moved to opposite
ends of cell.
Telophase II  Sex Cells
• Nucleus begins to
reform.
• Cytokinesis takes
place.
• Four haploid sex cells.
• Remember…
Sex cells = gametes = germ cells
Meiosis Overall
Males vs. Females
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MEN
Spermatogenesis
Starts at puberty
Testes
Four sperm cells
• Can produce
sperm until death
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WOMEN
Oogenesis
Starts at puberty
Ovaries
One egg & three
polar bodies
Stops at
menopause
Males vs. Females
Meiosis vs. Mitosis
Meiosis vs. Mitosis
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MEIOSIS
Sex cells
Two rounds of
division
Haploid cells
Results in four
cells
Genetically
different
Tetrads present
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MITOSIS
Body cells
One round of
division
Diploid cells
Results in two
cells
Genetically
identical
No tetrads here
That’s All I Got