Mrs. Stewart
Biology I standard
REVIEW:
 Cell Cycle
 Interphase

G1, S, and G2
 M-phase (mitosis)
 P-M-A-T-C
 Mitosis
 Asexual reproduction
 Produces 2 identical daughter cells
 Daughter cells are diploid
 Daughter cells are identical to parent/mother cell
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?
MEIOSIS:
 The process of creating a gamete
Chromosomes come in matching sets
-these are called homologous pairs
Karyotype
after DNA
replication
Notice how
each
chromosome
has
duplicated
itself.
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
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
 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
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
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
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
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
Oogenesis – meiosis in human female
reproductive cells – makes eggs (ovum)
• Forms one egg
cell with a large
supply of stored
nutrients.
• The other 3
gametes
produced, called
polar bodies,
disintegrate.
Spermatogenesis – meiosis in human male
reproductive cells to make sperm (spermatazoa)
• Produces 4
viable gametes
• All 4 gametes
produce a long
whip-like tail
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
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
Human chromosomal diseases
 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])
**Mistake in meiosis can lead to an incorrect chromosomal number, causing
consequences for offspring**
Video
 Meiosis square dance