Mitosis vs. Meiosis
No sex vs. Sex
Which is better?
Mr. Snider
SOCES
socesbio.com
Why do Mitosis?
• Growth 1 cell to billions exponentially
• Maintenance – replace skin, stomach
• Repair- injuries
Why do Meiosis?
• Variation – not FUN
– Remember over 50% of sexual reproduction
does not include intercourse
Mitosis vs. Meiosis
• One cell forms 2
exact copies
• 100% of DNA same
• Represent all genes
in gene pool
• Clones
• Susceptible to same
diseases
• 1 cell forms 4
daughter cells, each
with ½ the original #
of chromosomes
• Genetic
recombination
• Increase variation
• New combinations
Quick video comparison
http://www.youtube.com/watch?v=Ba9LXKH2ztU
Physical structure vs. genetics
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Physically Meiosis and Mitosis are similar
IPMAT
Interphase
Prophase
Metaphase
Anaphase
Telophase (Cytokenesis)
Mitosis preview – bear with 5 mins
• Awesome video
http://www.youtube.com/watch?v=Q6ucKWIIFmg
Interphase
• Common to both
Mitosis and Meiosis
• DNA and organelles
copy themselves
• G1 – growth 1
recovery (stop and
stay)
• S – synthesis copying
• G2 – growth 2 get beg
for copying (stop)
Prophase
• Chromatin condenses to
become visible as
chromosomes (sister
chromatids)
• Nuclear envelope breaks
apart
• Spindle apparatus
(spindle fibers and
centrosome) forms
spindle fibers=microtubules
Animal cell centrosome includes
centromere
Metaphase
• Sister chromatids line
up in the center of the
cell
• (spindle apparatus is
fully formed)
Anaphase
• Sister chromatids
separate, and
chromosomes
(chromatids) move to
the poles
Telophase (+cytokenesis)
• Spindle apparatus
dissolves
• Nuclear envelope reforms
• Chromosomes dissolve
into chromatin
• Cytokenesis – even
division of organelles
between daughter cells
• Cleavage plane in
animals
• Cell plate in plants
Summary Mitosis
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One cell forming 2 identical daughter cells
Growth, Maintenance, repair
Zygote- you 1000X
Cloning; Asexual
Reproduction – yeast?; single celled
protists (not bacteria – binary fission)
Review Mitosis
http://www.youtube.com/watch?v=kRWnJd1WRbA
Main Differences
• Mieosis – variation for offspring- gene
reduction
• Mitosis – perfect copies to get big enough
to do reproduction
• Question – which needs more energy?
• How many times to do reproduction?
Meiosis
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Diploid cell to haploid gamete
Diploid = 2 copies of chromosomes(2N)
Haploid = 1 copy (N or 1N)
If you add 2N+2N during sex BAD things
happen, so you must reduce 1st
• 2 times = Interphase +Meiosis 1 (P-T) +
Meiosis 2 (P-T) = 9 phases
• DNA changes only – physical parts same)
Interphase
• Same as in Mitosis – DNA and organelles
double (DNA during S phase)
Meiosis I
• Prophase – Tetrads
become visible
• Tetrad = Homologous
pair or Homologous
chromatids
• 2 pairs of sister
chromatids that have
same genes from
different parents
• Crossing over occurs
here
Metaphase I
• Tetrads line up in
center of cell
Anaphase I
• Tetrads (2 N)
separate and Sister
chromatids/
Homologous pairs (N)
move to the poles
• This is tricky – you
only have one set of
chromosomes, but 2
copies of that set
Telophase I
• Homologous pairs/
Sister Chromatids
sometimes
uncondense (most
don’t- loss of Energy)
Interphase II
• It’s a trick – don’t fall for it! No such thing!
Prophase II
• (Rest is same as
Mitosis)
• Sister chromatids/
Homologous pairs
attach to spindle
apparatus
Metaphase II
• Sister chromatids/
Homologous pairs
line up in center of the
cell
Anaphase II
• Sister chromatids/
Homologous pairs
separate and
Chromasomes/
Chromatids move to
poles
Telophase II (+Cytokenesis)
• Chromosomes
dissolve into
chromatin
• 4 daughter cells, each
with ½ original # of
chromosomes
Meiosis video
http://www.youtube.com/watch?v=kVMb4Js99tA
Summary (yet again)
• Mitosis – 1 cell forms
2 exact copies
• Asexual reproduction;
cloning
• Growth, maintenance,
repair
• Mutations lead to
uncontrolled cell
growth = cancer
• Meiosis- 1 cell forms 4
daughter cells, each with
½ the original # of
chromosomes
• Sexual reproduction
• Gamete production
(sperm, egg)
• Mutations lead to dead
offspring of changes in
gene frequency
(evolution)
Advice
• Follow up on youtube –
mitosis vs. meiosis videos; there are
several good ones.
http://www.youtube.com/watch?v=_llXzrz8oOc