Do Now
• What is the purpose of Mitosis?
• If a cell that has 12 chromosomes in
interphase goes through mitosis, how
many chromosomes will be in each cell?
• How is a baby made? (on a CELLULAR
level…)
Objectives
• To list the steps of Meiosis.
• To compare and contrast Meiosis and
Mitosis.
• To explain why Meiosis is necessary.
Meiosis
• Purpose: to make sex cells
– Gamete: sex cell
• Male gamete= sperm
• Female gamete= egg (ovum)
Lets take a look at our cells
• Our somatic cells contain 46
chromosomes
– 1 chromosome from Mom, and 1 from Dad.
These are called homologous chromosomes.
• Each gamete (sex cell) contains only 23
chromosomes!
• Why are there are only 23 chromosomes
in our sex cells?
Do Now
Check which box applies to the
following statements or terms.
Gamete Cell Somatic Cell
1. Lung Cell
2. Liver Cell
3. Sperm Cell
4. Cell with 23 chromosomes
5. Cell with 46 chromosomes
6. Egg Cell
Do Now – Period 3
• What is the sex of
this patient?
• Monosomy,
Trisomy?
• Is this individual
normal?
Objectives
• To create a karyotype.
• To determine if your client has down
syndrome, or another genetic disorder.
• To list the steps of meiosis.
• To explain the role of meiosis in life.
Homologous Chromosomes
• 23 pairs of _____________ chromosomes
– homologous: 1 from mom and 1 from dad, both
contain the same _________________.
• Mitosis creates cells that are ____________ (2n)
–_____________ = _____of each chromosome
Homologous Chromosomes
–Meiosis creates gametes that contain
______ chromosomes
• Gametes are _____________
–____________= only contain 1 of
each chromosome.
Diploid vs. Haploid
• Diploid cell
– Any cell with 2 homologous chromosomes
– Abbreviated as 2n
• Haploid cell
– Any cell with a single chromosome set
– Abbreviated as n
Do Now
Check which box applies to the
following statements or terms.
Haploid
1.Human Blood Cell
2. Somatic Cell
3. Sperm Cell
4. Cell with 23 chromosomes
5. Cell with 46 chromosomes
6. Gamete
Diploid
Objectives
• 1. SWBAT discuss the stages of meiosis
2. SWBAT draw and label the stages of
meiosis
• 3. SWBAT will compare and contrast
mitosis and meiosis
How do we become a Diploid
Zygote?
• Haploid egg cell fuses with haploid sperm cell
in a process called Fertilization.
• Half from mom and half from dad make up our
homologous chromosomes! (23 pairs)
• Our cells then undergo mitosis to create us.
• But how did our parents create the sex cells
to produce us?
Meiosis
• Meiosis I and Meiosis II
• Each are similar to
mitosis
• Produces 4 daughter
cells
• Phases are still IPMAT,
however there are two
of each of the PMAT
phases.
Prophase I
• Pairing of homologous
chromosomes occurs
forming a tetrad.
(synapsis)
• Nuclear envelope breaks
down.
• Crossing over can occurhomologous
chromosomes exchange
genetic material.
Metaphase I
• Chromosome
centromeres attach to
spindle fibers
• Homologous
chromosomes line up
at the equator.
Anaphase I
• Homologous
chromosomes
separate and move to
opposite poles
Telophase I
• The spindles break
down.
• Chromosomes uncoil
and form two nuclei.
• The cell divides.
Prophase II
• A second set of
phases begins as the
spindle apparatus
forms and the
chromosomes
condense.
Metaphase II
• A haploid number of
chromosomes line up
at the equator
• Sister chromatids line
up
Anaphase II
• The sister chromatids
are pulled apart at the
centromere by spindle
fibers
• Move toward the
opposite poles of the
cell.
Telophase II
• The chromosomes
reach the poles, and
the nuclear
membrane and nuclei
reform.
Cytokinesis
 Cytokinesis results in
four haploid cells
 Each with n number
of chromosomes.
 http://highered.mcgra
whill.com/sites/007249
5855/student_view0/c
hapter3/animation__h
ow_meiosis_works.ht
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