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There is a Need for Cell Division

During development


For the fertilized egg to divide into a
multicellular organism
In adults

To repair damage, and replace worn out cells
 And is needed in reproduction
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
1
Mitosis & Cytokinesis
Interphase
Mitosis
Prophase
(late Prophase)
Metaphase
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
Anaphase
Telophase and
cytokinesis
2
Term: Homologous Chromosomes


46 chromosomes are arranged in 23 pairs

One came from each parent

Talking only about humans
22 pairs are autosomes


Both chromosomes are homologs
1 pair are sex chromosomes
 XX
-females XY -males (~homologs)
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
3
Meiosis

Used to make gametes
 Eggs


Meiosis
and sperm
2n
Chromosome number is halved
(haploid)
Zygote is diploid after fertilization
n
Fertilization
2n
Mitosis
2n
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
4
Meiosis I vs. Mitosis
Prophase
Metaphase
Anaphase
Telophase and
cytokinesis
Mitosis
Prophase
Meiosis
Metaphase
Anaphase
In Anaphase,
Sister Chromatids
Separate,
diploid
Telophase and
cytokinesis
Sister Chromatids
remain attached,
Homologs separate
haploid
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
5
Meiosis II
Metaphase II
(prophase II not shown)
Anaphase II
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
Telophase II & Cytokinesis
6
Meiosis vs. Mitosis







Mitosis 1 cell into 2
Meiosis 1 cell into 4
Mitosis daughter cells remain diploid
Meiosis cells become haploid
Mitosis in anaphase, sister chromotids
separate.
Meiosis in anaphase I, homologs separate,
cells destined to become haploid.
Mitosis for cell replication including asexual
reproduction, meiosis for sexual reproduction
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
7
Telophase I/Prophase II
Complication
1. I have kept things simple.
2. In some species, cytokinesis begins before
telophase I or II end.
3. Different species perform different things in
telophase I, cytokinesis, & prophase II of meiosis.
4. Example, some species never reform the nuclear
membrane in telophase I, so they do not degrade
it in prophase II. We will keep things simple.
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
8
Concept Quiz
Meiosis insures that
A.
Each gamete receives the same genes
B.
Chromosome number is doubled in the
gametes
C.
Zygotes produced by fertilization have the
normal number of chromosomes
D.
All paternal chromosomes end up in the same
gamete
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
9
Review
Animation on The Cell Cycle
mitosis on web
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
10
Review
Mitosis and Cell Division
 Mitosis movie (shown
in lab)

If does not work, email me.

Meiosis movie
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
11
In Class Activity

If time, start in class activity on mitosis &
meiosis.
© 2006 W.W. Norton & Company, Inc.
DISCOVER BIOLOGY 3/e
12