MEIOSIS
Chapter 12
Honors Genetics
Slide show modified from Kelly Riedell, Tracy Jackson and Kim Foglia
BINARY FISSION & MITOSIS
Produces cells that are genetically
identical
__________
copies of parent
cell
Asexual vs. Sexual
Reproduction
In asexual reproduction
One parent produces genetically identical
offspring by mitosis
Ex: budding, binary fission, spores, etc.
Parent
Bud
0.5 mm
ADVANTAGES OF
ASEXUAL REPRODUCTION
• Can make offspring
faster
• Don’t need a
partner; only 1
“parent” needed
DISVANTAGES OF
ASEXUAL REPRODUCTION
• ALL ALIKE (“clones”)
• Species usually
CAN’T change and
adapt
• One disease can
wipe out whole
population
SEXUAL
REPRODUCTION
• Combines genetic material from 2 parents
(sperm & egg)
• Offspring are genetically different
and unique from parents
ADVANTAGES OF
SEXUAL REPRODUCTION
• Allows for variation in population
• Individuals can be different
• Provides foundation for EVOLUTION
• Allow species adapt to changes in their
environment
EGG
+
SPERM 
If egg and sperm had same number of
chromosomes as other body cells (2n) . . .
baby would have too many chromosomes!
MEIOSIS is the way…
to make cells
with ½ the
number of
chromosomes
for sexual
reproduction
http://waynesword.palomar.edu/lmexer2a.htm
DIPLOID
Most cells have 2 copies of each chromosome
DIPLOID
2n
= ______________
(one from mom; one from dad)
HOMOLOGOUS
CHROMOSOMES
All BODY (________
SOMATIC ) cells are diploid
Chromosomes that
determine the sex of
an organism =
Sex chromosomes
_________________
All other chromosomes
that do NOT determine
autosomes
gender = __________
Humans have two sex chromosomes (1 pair),
which are NOT homologous
44 autosomes
and _____
XX or XY
HAPLOID
Some cells have only one copy of each
HAPLOID
1n
chromosome = _____________
All sperm and egg cells
are haploid
Review…MITOSIS
• Makes ___
2 cells genetically
identical
_________
to parent cell &
to each other
2n
• Makes ___ cells
• Makes __________
SOMATIC (body)
• Used by organisms to:
increase size of organism,
repair injuries,
replace worn out cells
http://waynesword.palomar.edu/lmexer2a.htm
MEIOSIS
4 cells
• Makes ____
genetically different
from parent cell & from
each other
1n cells
• Makes _____
• Makes ______________
Gametes
(sperm & eggs)
Sexual reproduction
• Used for ____________
http://waynesword.palomar.edu/lmexer2a.htm
2
karyokinesis
events occur
in meiosis!
WHAT MAKES MEIOSIS
DIFFERENT FROM MITOSIS
? 1
1. 2 divisions instead of
–
Meiosis I and Meiosis II (PMATc I & PMATc II)
2. SYNAPSIS & CROSSING OVER
(PROPHASE I)
1. INDEPENDENT ASSORTMENT and
SEGREGATION
(ANAPHASE I)
1. 4 cells are made and they are haploid
2. Daughter cells are genetically
DIFFERENT
WHAT MAKES MEIOSIS
DIFFERENT FROM MITOSIS?
1. Homologous chromosomes pair up
during ________________
PROPHASE I
called SYNAPSIS
= ______________
This group of FOUR (4)
chromatids is called a
TETRAD
_________________
Images modified from: http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif
WHAT MAKES MEIOSIS
DIFFERENT FROM MITOSIS?
1. Exchange of DNA between
OVER
homologous pairs = CROSSING
_____________
during PROPHASE I
Allows shuffling
of genetic material
called genetic
recombination
Place(s) where crossing over
happens
CHIASMATA
= ____________________
http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter12/animations.html#
CROSSING
OVER
rearranging of DNA
• Allows for_________________
in different combinations
• After crossing over, chromatid arms
NOT IDENTICAL anymore
are________________
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
INDEPENDENT ASSORTMENT
the random alignment of homolgous chromosome
pairs at metaphase plate (Metaphase I)
http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg
SEGREGATION
separating of doubled chromosomes
(homologous pairs)
(Anaphase I)
SEGREGATION & CROSSING OVER
together make even more gamete combinations
See an
animation
http://waynesword.palomar.edu/lmexer2a.htm
INDEPENDENT ASSORTMENT
and SEGREGATION
at METAPHASE/ANAPHASE I
Lots of different
combinations are
possible!
3rd animation
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter12/animati
This is why you
don’t look exactly
like your brothers
and sisters even
though you share
the same parents!
GENETIC RECOMBINATION
comes from:
• Crossing over
• Segregation
• Independent assortment
• Random fertilization
PHASES OF MEIOSIS
Figure 11-15 Meiosis
Section 11-4
Meiosis I
= MAJOR differences from mitosis
Meiosis II:
Figure 11-17 Meiosis II
NOTEno Interphase II- instead short intermission
Section 11-4
(no growth or DNA replication occurs)
Prophase II
Meiosis I results in two
haploid (N) daughter cells,
each with half the number of
chromosomes as the original.
Metaphase II
Anaphase II
Telophase II
The chromosomes line up in a
similar way to the metaphase
stage of mitosis.
The sister chromatids
separate and move toward
opposite ends of the cell.
Meiosis II results in four
haploid (N) daughter cells.
MITOSIS vs. MEIOSIS
INTERPHASE
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
2n cell
•
•
•
•
•
INTERPHASE I
2n cell
DNA is spread out as chromatin
Nuclear membrane/nucleolus visible SAME AS
DNA is copied during S phase
MITOSIS
Makes stuff new cell needs in G2
Cell Grows
MITOSIS vs. MEIOSIS
PROPHASE
PROPHASE I
2n cell
2n cell
•
•
•
•
• DNA packs into chromosomes
DNA packs into
• Nuclear membrane/ nucleolus
chromosomes
disappear
Nuclear membrane/
• Spindle fibers appear and attach
nucleolus disappear
to chromosomes
Spindle fibers appear and
• Centrosomes migrate to poles
attach to chromosomes
SYNAPSIS and CROSSING
Centrosomes migrate to poles
OVER OCCURS
MITOSIS vs. MEIOSIS
METAPHASE
2n cell
• Chromosomes line up
in middle in single file
line
METAPHASE I
2n cell
•Chromosomes line up
in middle with
homologous partner
•Independent
assortment occurs
MITOSIS vs. MEIOSIS
ANAPHASE ANAPHASE I
2n cell
• Polar fibers
lengthen cell
• Chromatids split
2n cell
•Polar fibers lengthen cell
•Chromatids stay together
Homologous pairs split
(SEGREATION OCCURS)
MITOSIS vs. MEIOSIS
TELOPHASE TELOPHASE I
2n cell
•
•
•
•
n cell
See TWO nuclei
Nuclear membrane/ nucleolus return
SAME AS
DNA spreads out as chromatin
MITOSIS
Spindle fibers disappear
MITOSIS vs. MEIOSIS
CYTOKINESIS
2n cell
DIPLOID
Cytoplasm splits
into 2 cells using
CYTOKINESIS I
n cell
HAPLOID
SAME AS
MITOSIS
MITOSIS vs. MEIOSIS
INTERPHASE II
2n cell
•
•
•
•
•
DNA is spread out as chromatin
Nuclear membrane/nucleolus visible
DNA is copied during S phase
Makes stuff new cell needs in G2
Cell Grows
n cell
SKIP
INTERPHASE II
DNA NOT
COPIED
MITOSIS vs. MEIOSIS
PROPHASE
PROPHASE II
n cell
2n cell
•
•
•
•
DNA packs into chromosomes
Nuclear membrane/ nucleolus
disappear
Spindle fibers appear and attach
to chromosomes
Centrosomes migrate to poles
SAME AS
MITOSIS
(but cell is now
HAPLOID)
MITOSIS vs. MEIOSIS
METAPHASE
METAPHASE II
n cell
2n cell
• Chromosomes line up
in middle in a single
file line
SAME AS MITOSIS
(but cell is now HAPLOID)
MITOSIS vs. MEIOSIS
ANAPHASE ANAPHASE II
2n cell
Chromatids split and
move apart
n cell
SAME AS MITOSIS
(but cell is now HAPLOID)
MITOSIS vs. MEIOSIS
TELOPHASE
TELOPHASE II
2n cell
n cell
• See TWO nuclei
• Nuclear membrane/
nucleolus return
• DNA spreads out as
chromatin
SAME AS MITOSIS
• Spindle fibers disappear (but cell is now HAPLOID)
MITOSIS vs. MEIOSIS
CYTOKINESIS CYTOKINESIS II
RESULTS IN
FOUR
n cell
RESULTS IN
TWO
2n cell
Cytoplasm splits
SAME AS MITOSIS
(but cell is now HAPLOID)
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Ways Meiosis is
different?
• 2nd and 4th animations
– http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter12/an
imations.html#
MAKING
SPERM &
EGGS
• Gametogenesis =
– process of forming gametes (n) from
diploid (2n) cells
2 TYPES:
• Spermatogenesis =
process of forming sperm cells
• After division all 4 cells undergo
differentiation to become sperm cells
• The cells elongate and grow tail (a flagella)
• Oogenesis =
process of forming ovum (egg) cell and
3 polar bodies
Starts with a 2n
cell called a
GERM LINE CELL
SPERMATOGENESIS
___________________=
MAKING MATURE SPERM
Mature & grow flagella
•Sperm provides DNA to the zygote.
•All the starting nutrients, organelles,
molecule building blocks, etc. have to come
from the ovum (egg)
OOGENESIS
__________________
=
MAKING a MATURE EGG
Produces:
1 “good”
ovum (egg)
3
POLAR BODIES
•CYTOPLASM DIVIDES UNEVENLY
•Polar bodies are smaller and are later
destroyed using APOPTOSIS
Stages of Meiosis
STEP by STEP animation
• http://www.stolaf.edu/people/giannini/flashani
mat/celldivision/meiosis.swf
Putting it all together…
meiosis  fertilization  mitosis + development
46
23
egg
23
46
sperm
46
46 46
46 46 46
4646 46
What happens when meiosis goes wrong?
 NONDISJUNCTION!!!
Meiosis Animations
Frame-by-frame animation
http://www.csuchico.edu/~jbell/Biol207/animations/
meiosis.html