1. 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

2. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Mitosis & Cytokinesis
Interphase
Mitosis
Prophase
(late Prophase)
Metaphase
Anaphase
Telophase and
cytokinesis
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

3. 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

4. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Meiosis
Used to make gametes
Eggs and sperm
Chromosome number is halved (haploid)
Zygote is diploid after fertilization
Meiosis 2n n
Fertilization 2n
Mitosis 2n
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

5. Meiosis I vs. Mitosis In Anaphase, Sister Chromatids Separate, diploid
Prophase
Metaphase
Anaphase
Telophase and
cytokinesis
Mitosis
Meiosis
In Anaphase, Sister Chromatids
Separate,
diploid
Sister Chromatids
remain attached,
Homologs separate
haploid
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

6. Meiosis II (prophase II not shown)
Metaphase II
Anaphase II
Telophase II & Cytokinesis
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

7. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
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

8. Telophase I/Prophase II Complication
I have kept things simple.
In some species, cytokinesis begins before telophase I or II end.
Different species perform different things in telophase I, cytokinesis, & prophase II of meiosis.
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.
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9. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Concept Quiz
Meiosis insures that
Each gamete receives the same genes
Chromosome number is doubled in the gametes
Zygotes produced by fertilization have the normal number of chromosomes
All paternal chromosomes end up in the same gamete
The correct answer is C. This is the key to meiosis – reduction division so that the fertilized egg restores the normal number of chromosomes.
Answer A: Each gamete doesn’t receive the same genes because the homologous chromosomes are randomly assorted during meiosis I.
Answer B: Chromosome number is halved in the gametes.
Answer D: As in the answer for A, the homologous chromosomes are randomly assorted during meiosis I.
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

10. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Review Animation on The Cell Cycle
mitosis on web
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

11. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
Review
Mitosis and Cell Division
Mitosis movie (shown in lab)
If does not work, me.
Meiosis movie
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e

12. © 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e
In Class Activity
If time, start in class activity on mitosis & meiosis.
© 2006 W.W. Norton & Company, Inc. DISCOVER BIOLOGY 3/e