4. What differences
can you see?
• How many sets of
chromosomes are in
the cells that
Meiosis produces?
• How many cells
does Meiosis
produce?
• How many
divisions occur
in Meiosis?
5. Final Products:
Mitosis
Somatic cells in your body have
two sets of chromosomes they are called DIPLOID
Meiosis
Gametes (Sex cells-sperm and
eggs) only have one set (half)
of chromosomes - they are
called HAPLOID
7. What are the steps?
Phases of Meiosis I
Prophase I
Metaphase I
Anaphase I
Telophase I
Cytokinesis
Interkinesis
Phases of Meiosis II
Prophase II
Metaphase II
Anaphase II
Telophase II
Cytokinesis
10. DNA replicates
Interphase
Makes the diploid
(2n) cell now be (4n)
n=number of
chromosome
sets/pairs
Example: humans
have 46 total
chromosomes, so our
diploid number is 2n
or 2(23) where n = 23
13. Prophase I
• Homologous
chromosomes pair
up (forming a
tetrad) - Mom &
Dad go on a date
• Crossing over
occurs
• Chromatids
MAY exchange
portions of
DNA
• Leads to
genetic
variances
14. Prophase I
Homologs (homologous
pairs of chromsomes)
form Tetrads
Crossing Over occurs
15. Metaphase I
Spindle fibers attach to the chromosomes
Homologous chromosomes line up in the middle of
the cell
Anaphase I
• Fibers pull the homologous chromosomes toward
opposite ends of the cell
Telophase I and Cytokinesis
• Nuclear membranes form
• Cell separates into two new cells
18. Meiosis II
The daughter cells from Meiosis I
divide again WITHOUT replicating
their chromosomes
That leads to 4 gametes, each with half
the number of chromosomes (haploid)
as the original “mother” cell
19. Prophase II
Spindle fibers form and move chromosomes to center
Metaphase II
Spindle fibers attach to the chromosomes
chromosomes line up in the middle of the cell – similar to
how they do in Mitosis
Anaphase II
• Fibers pull the sister chromatids toward
opposite ends of the cell
Telophase II and Cytokinesis
• Nuclear membranes form
• Both cells separate – forming 4 new haploid cells
20.
21. Oogenesis – meiosis in human female
reproductive cells – makes eggs (ovum)
• Total of 4 cells
produced:
• Forms one
usable egg cell
with a large
supply of stored
nutrients.
• The other 3 cells,
called polar
bodies,
disintegrate.
22. Spermatogenesis – meiosis in human male
reproductive cells to make sperm (spermatazoa)
• Produces 4
viable gametes
• All 4 gametes
produce a long
whip-like tail
23. Meiosis:
Cell division necessary for sexual reproduction
Produces 4 daughter cells
Daughter cells are Haploid
Daughter cells are gametes (sexual repro. cells)
2 nuclear/cellular divisions
Vital to maintain correct number of offspring in
sexually reproducing organisms
Crossing over = opportunity for genetic variability
24. Differentiate
Mitosis
Meiosis
Asexual reproduction
Used for sexual reproduction
Produces 2 daughter cells
Produces 4 daughter cells
Daughter cells are diploid
Daughter cells are Haploid
Daughter cells are
Daughter cells are genetically
identical to each other
and to parent cell
Produces somatic cells
One cell/nuclear division
different from each
other, and from parent cell
Produces gametes
Two nuclear/cellular divisions
25. Human chromosomal diseases
**Mistake in meiosis can lead to an incorrect
chromosomal number, causing
consequences for offspring**
Down’s syndrome (extra chromosome #21)
Turner’s syndrome (missing or incomplete X
chromosome in girls)
Klinefelter’s syndrome (males that have an extra X
chromosome [XXY])
26. Think – Pair – Share
How does a baby with Down’s Syndrome
end up with 3 chromosome #21s?