From Egg to Embryo – This
photograph - 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.
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In order to study genetics, we must
first understand how the genes get
passed on to offspring.
The process of meiosis makes
gametes [aka sperm and egg]
which contain the genes to make a
new organism.
This unit will introduce you to the
process of meiosis, a form of cell
division similar to mitosis; summary
color is blue and vocabulary words
are underlined.
Video
http://nevinerk.weebly.com/uploads/5/2/9/9/5299320/
8932292.png?333
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Meiosis is the process by which
the # of Xsomes is reduced by ½
forming gametes EX sperm or
eggs.
 2 cell divisions
 Occurs in the sex organs
[ovaries and testicles]
▪ Meiosis animation
http://www.wereyouwondering.com/wpontent/uploads/2008/06/meiosisi
magecreditnih.jpg
http://www.polyvore.com/cgi/img-thing?.out=jpg&size=l&tid=11193462
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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.
https://upload.wikimedia.org/wikipedia/commons/thumb/e/e0/Major_events_in_mitosis.svg/350pxMajor_events_in_mitosis.svg.png
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 sex cells are haploid.
https://upload.wikimedia.org/wikipedia/commons/thumb/9/9a/Meiosis_Overview.s
vg/2000px-Meiosis_Overview.svg.png
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"Normal meiosis and nondisjunction." Genetics. Ed. Richard Robinson. New York: Macmillan
Reference USA, 2010. Science in Context. Web. 3 Dec. 2013.
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
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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.
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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.
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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.
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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
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? What does
that mean about the diploid versus haploid
number for this organism? Turn and talk to
your neighbor.
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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.
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
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
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.