Download 03 Meiosis Lesson

MEIOSIS
(the formation of sex cells)
Purpose of Meiosis
The purpose of meiosis is to produce gametes or
sex cells (sperm and egg cells) with half the number
of chromosomes as the original cell.
In humans, each gamete contains only 23
chromosomes.
This ensures that when sperm and egg cells combine
the resulting cell (a zygote) will have the same
number of chromosomes as the original cell (46
chromosomes).
Overview of Meiosis
• During meiosis cells
divide twice, unlike
mitosis where there is
only one cell division.
• As a result, 4 cells are
produced instead of 2.
Mitosis
Meiosis
However, the process of meiosis is different in
males and females.
Spermatogenesis
(the formation of sperm cells)
• In males, meiosis takes
place in the testes
• Each of the four haploid
cells produced develop
into sperm cells
• Healthy men can produce
sperm from puberty until
the day they die.
Pierre Elliot Trudeau, former Prime Minister of Canada fathered a child
when he was 72 years old!
Oogenesis
(the formation of egg cells)
• In females, meiosis takes
place in the ovaries
• Each time the cells split
the cytoplasm is divided
unevenly
• This results in one large
cell and three tiny cells
(polar bodies)
• Only the large cell
survives and becomes an
egg cell
Unlike men, women are born with all of the egg cells they will ever have!
They release one egg a month (on average) during menstruation. When all of
their eggs are gone they enter menopause.
Comparing Mitosis and Meiosis
Produces
# of chromosomes
in the cells produced
Cells produced are
Mitosis
2 body cells
Meiosis
4 sex cells
46
23
Identical to
each other and
to the parent
cell
unique