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MEIOSIS
http://waynesword.palomar.edu/lmexer2a.htm
Remember from Chapter 1:
CHARACTERISTICS OF LIVING THINGS
REPRODUCE
ALL LIVING THINGS __________
ASEXUAL
Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm
Family http://babyhearing.org/Parenet2Parent/index.asp
SEXUAL
ASEXUAL REPRODUCTION
Bacteria reproduce using
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookmito.html
BINARY FISSION
__________________________________
http://fig.cox.miami.edu/~cmallery/150/mitosis/c7.13.2.hydra.jpg
Budding & regeneration are used by plants
and animals to reproduce asexually
(mitosis)
Planaria animation: http://www.t3.rim.or.jp/~hylas/planaria/title.htm
BINARY FISSION & MITOSIS
identical
Produces cells that are __________
copies of parent cell
ADVANTAGES OF
ASEXUAL REPRODUCTION
Can make offspring
faster
Don’t need a partner
http://www.mrgrow.com/images/cutting.jpg
DISVANTAGES OF
ASEXUAL REPRODUCTION
ALL ALIKE
Species CAN’T
change and adapt
One disease can wipe
out whole population
http://www.mrgrow.com/images/cutting.jpg
SEXUAL REPRODUCTION
Family image from: http://babyhearing.org/Parenet2Parent/index.asp
Combines genetic material
from 2 parents (sperm & egg)
Offspring are genetically
different 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
http://naturalsciences.sdsu.edu/classes/lab8/spindex.html
Image by Riedell
EGG
Image by Riedell
+
http://www.angelbabygifts.com/
SPERM 
If egg and sperm had same number of
chromosomes as other body cells . . .
baby would have too many chromosomes!
http://www.acmecompany.com/stock_thumbnails/13217.forty-six_chromosomes.jpg
MEIOSIS is the way…
http://waynesword.palomar.edu/lmexer2a.htm
to make cells
with ½ the
number of
chromosomes
for sexual
reproduction
DIPLOID & HAPLOID
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
http://www.angelbabygifts.com/
All other chromosomes =
_________________
autosomes
Humans have two sex chromosomes
X
y
and _____
44 autosomes
KARYOTYPE is a picture of
A __________
an organism’s chromosomes
DIPLOID & HAPLOID
Some cells have only one copy of each
HAPLOID
1n
chromosome = _____________
All sperm and egg cells
are haploid
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 ______________
Germ cells
OR Gametes (sperm & eggs)
• Used for ____________
sexual
reproduction
http://waynesword.palomar.edu/lmexer2a.htm
What Makes Meiosis Different?
Meiosis Lecture 2
WHAT MAKES MEIOSIS
DIFFERENT ?
1. SYNAPSIS & CROSSING OVER
(PROPHASE I)
2. SEGREGATION &
INDEPENDENT ASSORTMENT
(ANAPHASE I)
3. Skip INTERPHASE II (NO S)
CELL DIVIDES TWICE, BUT…
ONLY COPIES DNA ONCE
WHAT MAKES MEIOSIS
DIFFERENT ?
1. Homologous chromosomes pair up
during ________________
PROPHASE I
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?
1. Exchange of DNA between
OVER
homologous pairs = CROSSING
_____________
during PROPHASE I
Allows shuffling
of genetic material
Places where crossing over
happens
CHIASMATA
= ____________________
http://www.emc.maricopa.edu/faculty/farabee/BIOBK/Crossover.gif
HOMOLOGOUS CHROMOSOMES
Image modified by Riedell
• SAME SIZE
• SAME SHAPE
• CARRY GENES for the
SAME TRAITS
IDENTICAL
• BUT NOT
______________!
(Don’t have to have the
SAME CHOICES)
http://sps.k12.ar.us/massengale/genetics%20tutorial.htm
Image modified by Riedell
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
SEGREGATION
(Anaphase I)
• Orientation of the
chromosome pairs is random
with respect to the poles
• Separation of homologous
chromosomes ensures that
each gamete receives a
haploid set of chromosomes
composed of both maternal
and paternal chromosomes
SEGREGATION & CROSSING OVER
together make even more combinations
See an
animation
http://waynesword.palomar.edu/lmexer2a.htm
INDEPENDENT ASSORTMENT
http://fig.cox.miami.edu/~cmallery/150/mitosis/c13x9independent-assortment.jpg
INDEPENDENT ASSORTMENT
at ANAPHASE I
Lots of different
combinations are
possible!
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
– fusion of two gametes, increase genetic
variation in populations by providing new
combinations of genetic information in
the zygote, and restores diploid number
of chromosomes
Phases of Meiosis
Figure 11-15 Meiosis
Section 11-4
Meiosis I
Figure 11-17 Meiosis II
Section 11-4
Meiosis II
Prophase II
Metaphase II
Anaphase II
Meiosis I results in two
The chromosomes line up in a The sister chromatids
haploid (N) daughter cells,
similar way to the metaphase separate and move toward
each with half the number of stage of mitosis.
opposite ends of the cell.
chromosomes as the original.
Telophase II
Meiosis II results in four
haploid (N) daughter cells.
MITOSIS vs MEIOSIS
INTERPHASE INTERPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA is spread out as chromatin
• Nuclear membrane/
nucleolus visible
• DNA is copied during S phase
• Makes stuff new cell needs in G2
SAME AS
MITOSIS
MITOSIS vs MEIOSIS
PROPHASE PROPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
DNA scrunches into
chromosomes
Nuclear membrane/
nucleolus disappear
Centrioles/
spindle fibers appear
DNA scrunches into
chromosomes
Nuclear membrane/
nucleolus disappear
Centrioles/
spindle fibers appear
Homologous pairs match up
MITOSIS vs MEIOSIS
METAPHASE
METAPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• Chromosomes line up
in middle
Chromosomes line up
in middle
with homologous partner
MITOSIS vs MEIOSIS
ANAPHASE ANAPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
APART:
Chromatids split
APART:
Chromatids stay together
Homologous pairs split
MITOSIS vs MEIOSIS
TELOPHASE TELOPHASE I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
See TWO nuclei
Nuclear membrane/
SAME AS MITOSIS
nucleolus return
DNA spreads out as chromatin
Spindle/centrioles disappear
MITOSIS vs MEIOSIS
CYTOKINESIS CYTOKINESIS I
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Cytoplasm splits
into 2 cells
SAME AS
MITOSIS
MITOSIS vs MEIOSIS
INTERPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA is spread out as chromatin
SKIP
• Nuclear membrane/
INTERPHASE II
nucleolus visible
• DNA is copied during S phase DNA NOT COPIED
MITOSIS vs MEIOSIS
PROPHASE PROPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• DNA scrunches into
chromosomes
• Nuclear membrane/
nucleolus disappear
• Centrioles/
spindle fibers appear
SAME AS MITOSIS
MITOSIS vs MEIOSIS
METAPHASE
METAPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
• Chromosomes line up
in middle
SAME AS MITOSIS
MITOSIS vs MEIOSIS
ANAPHASE ANAPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Chromatids split and
move apart
SAME AS MITOSIS
MITOSIS vs MEIOSIS
TELOPHASE TELOPHASE II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Two nuclei
Nuclear membrane/
nucleolus returns
Centrioles/spindle fibers
disappear
DNA spreads out as
chromatin
SAME AS MITOSIS
MITOSIS vs MEIOSIS
CYTOKINESIS CYTOKINESIS II
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
Cytoplasm splits
http://www.pbs.org/wgbh/nova/baby/divi_flash.html
SAME AS MITOSIS
Ways Meiosis is different?
• Homologous pairs match up & trade DNA
(SYNAPSIS & CROSSING OVER) in
PROPHASE I
•SEGREGATION
& INDEPENDENT ASSORTMENT
in Anaphase I
create genetic recombination
• Skipping INTERPHASE II(Dividing TWICE but copying DNA once)
produces 1n cells
Nondisjunction –
Failure of homologous chromosomes OR
chromatids to separate at anaphase
Mistakes in Meiosis
Meiosis Lecture 4
Nondisjunction
Results in ANEUPLOIDY =
one or more chromosomes have extra or missing copies
AFTER FERTILIZATION:
Cell with only 1 copy of a chromosome instead of 2
= MONOSOMY
Cell with 3 copies of a
chromosome instead of 2
= TRISOMY
• Errors in mitosis or meiosis can result in
changes in phenotype
– Changes in chromosome number often result
in:
• New phenotypes
– Sterility caused by triploidy and increased vigor of other
polyploids
• human disorders with developmental limitations
– Trisomy 21 (Down syndrome)
– XO (Turner Syndrome)
Karyotype can show:
•
•
•
•
Sex of baby
Missing or extra chromosomes
Major deletions or translocations
Can’t see individual gene changes
http://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Dow
Down syndrome (Trisomy 21)
Most common chromosomal
http://www.hadsa.org/
abnormality (1 in 800 births)
Similar facial features
Slanted eyes / Protruding tongue
Mild to severe mental retardation
50% have heart defects that need
surgery to repair
Both older (35+ years) and
younger (under 16 years)
mothers are more at risk.
Some individuals with Down syndrome have the normal
number of chromosomes but have all or part of a third
chromosome 21 attached to another chromosome by
translocation.
http://content.answers.com/main/content/wp/en/thum
Turner syndrome (X0)
http://medgen.genetics.utah.
1 in 5000 births
Females have only one X chromosome
Small size
Broad chest
Slightly decreased intelligence
35% have heart abnormalities
Hearing loss common
Reproductive organs don’t develop at puberty
Klinefelter syndrome
http://www.akdeniz.edu.tr/tip/histoloji/
1 in 2000 births live births
Males have extra X chromosomes
(Can be XXy, XXXy, or XXXXy)
Taller than average
Normal intelligence
have male sex organs, but are sterile.
may be feminine characteristics,
Often not discovered until puberty
when don’t mature like peers
Presence of BARR BODIES