From Egg to Embryo – This
photograph shows the After the
egg [shown in orange] is released
from the ovary, it travels into the
fallopian tube. It stays there until
a single sperm [shown in blue]
fertilizes it. This unit will explain
the process of meiosis in the
production of eggs and sperm;
summary color is blue and
vocabulary words are underlined.

Meiosis is the process by which
the number of chromosomes is
reduced by half forming gametes
EX sperm or eggs.
 Two cell divisions
 Meiosis animation
http://www.wereyouwondering.com/wp
ontent/uploads/2008/06/meiosisimagecreditnih.jpg

Meiosis creates haploid cells;
remember, you get half your
DNA from each of your parents.
 Haploid, n = a cell with only 1
copy of each chromosome; EX
"Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson.
sex cells are haploid.
New York: Macmillan Reference USA, 2010. Science in Context. Web. 3
Dec. 2013.

Mitosis creates IDENTICAL diploid cells.
 Diploid, 2n = a cell with 2 of each chromosome; EX
somatic [body] cells like skin cells or heart cells are
diploid.
How do the sketches to
the right visually
represent a diploid
versus a haploid cell?
Which is made by
mitosis versus which is
made by meiosis? Turn
and talk to your
neighbor.
http://www.personal.psu.edu/staff/d/r/drs18/bisciImages/ha
ploidDiploid.png

The stages of meiosis I are identical to the stages of cell cycle and
mitosis; there are only slight differences during prophase.
 After going through the steps of Meiosis I
1. Interphase 1
2. Prophase 1 [+ crossing over]
3. Metaphase 1
4. Anaphase 1
5. Telophase 1 + Cytokinesis
 Forms 2 diploid daughter cells.
 …the cell divides again! [AKA Meiosis II]
"Meiosis." Biology. Ed. Richard Robinson. New York: Macmillan
Reference USA, 2010.Science in Context. Web. 3 Dec. 2013.

AKA homologs are paired Xsomes with genes of the same
trait in the same order; within each pair, one chromosome
comes from each parent.
 Homologous chromosomes
are only found in a diploid cell.
"Result of Crossing Over." Genetics. Ed. Richard Robinson.
New York: Macmillan Reference USA, 2010. Science in
Context. Web. 3 Dec. 2013.
This a karyotype, a tool that
geneticists use to look for
mutations.
It groups the homologous
chromosomes in pairs; the
longest pair is #1, the shortest
pair is #22.
http://www.biotechnologyonline.gov.au/images/contentpa
ges/karyotype.jpg

During Prophase I, the
homologous chromosomes mix
genetic material [known as
crossing over].
 This is used to create new
combinations of genes – when
the cell is split in two, the
genetic material is now
different than the parent cell
due to crossing over.
 Allows for more variety within
organisms.
 Crossing Over Animation
http://www.chuvicky.estranky.cz/i
mg/picture/242/crossing_over.jpg
How do the sketches to
the right visually
represent crossing over.
Turn and talk to your
neighbor.

After meiosis I the cell divides again!
 This stage is different yet again,
because Xsomes are NOT copied
during Meiosis II.
 The stages are identical
(interphase, prophase,
metaphase, etc), but cells formed
have half (haploid) of the number
of Xsomes in the parent cells.
 Forms unique 4 haploid daughter
cells.
 Meiosis Animation
http://rationalwiki.org/w/images/thumb/b/b4/Mei
osis.gif/250px-Meiosis.gif
Name & Period at the
Top
What are the similarities
and differences between
the processes of mitosis
and meiosis?
List your answer in
bullet points on your
sticky note.
"Mitosis and meiosis." World of Anatomy and Physiology. Gale, 2010. Science in Context. Web.
4 Dec. 2013.
Use the play dough and the
chalk to show meiosis at your
tables.
 Our organism only has 2
chromosomes; use two colors
[do not completely mix
them].
 Show the following:
 Meiosis 1 Stages
 Crossing over
 Meiosis 2 Stages +
Cytokinesis
 Label the following:
 Diploid cell
 Haploid cell

How many chromosomes are at the
beginning of the diagram versus at the end?
Based on that information, how many would
go in each haploid daughter cell? Turn and
talk to your neighbor.

During meiosis, if homologous chromosomes fail to separate
correctly during anaphase (nondisjunction) then gametes have
either extra Xsomes or they are missing chromosomes.
 These mutations are passed on during fertilization [see image
to the right].
 Offspring with more than the usual #
of Xsomes are called polyploids.
▪ Rare in animals, sometimes causes death.
▪ Common in plants; polypoids are often healthier.
One of the most common examples of
polyploidy in humans is Trisomy 21 [extra
copy of chromosome 21]. These individuals
have Down syndrome.
http://www.geneticsofpregnancy.com/images/D
own_syndrome.jpg
http://static3.wikia.nocookie.net/__cb201206081
12249/glee/images/9/98/Becky_Jackson.png
How do the sketches to
the right visually
compare normal meiosis
versus nondisjunction.
Turn and talk to your
neighbor.
"Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson.
New York: Macmillan Reference USA, 2010. Science in Context. Web. 3
Dec. 2013.