1. Mitosis & Meiosis
Dr. Jeelan Moghraby
B.Sc., D.Phil
Assistant Professor
Email: moghrabyj@ksau-hs.edu.sa
PMED214 2013

2. Objectives
Cell Division
Phases of the cell cycle
Mitosis
Meiosis
Dr. J Moghraby
Meiosis

3. Cell Division
Continuity of life is based on the reproduction
of cells

4. Unicellular organisms: division of one cell reproduces
the entire organism
Multi-cellular organisms: growth, repair and
development of fertilized cell are dependent on cell
division
Dr. J Moghraby
division
Cell division results in genetically identical daughter
cells

5. Genetic Material of a Eukaryotic Cell
Dr. J Moghraby
© 2008 by Steven M. Carr, after original by Genetix
Somatic cells have two sets
of chromosomes
DNA packaged into
chromosomes consisting
of chromatin

6. Chromosomes
Chromosome
duplication
(including DNA
synthesis)
Chromo-
some arm
DNA molecules
Results in two
identical copies
called sister
chromatids that are
Duplication of DNA
Dr. J Moghraby
Sister
chromatids
Separation of
sister chromatids
Centromere
Sister chromatids
chromatids that are
connected by
centromeres

7. Phases of the Cell Cycle
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

8. SG
Control
system
G1 checkpoint
Cell Cycle Control
Three major
checkpoints
G1 checkpoint =
‘start’
Dr. J Moghraby
SG1
M checkpoint
G2M
system
G2 checkpoint
‘start’
Without correct signal
to pass the G1
checkpoint, exit the
cell cycle and enter
the non-dividing G0
phase

9. 2001 Nobel Prizes in Eukaryotic Cell Cycle
Hartwell Nurse Hunt
Dr. J Moghraby
Hartwell Nurse Hunt
Cell cycle checkpoints
Cyclin-dependent kinases
Cyclins

10. Most cells result in identical daughter cells (2n) in
process of mitosis and cytokinesis
Meiosis is a special type of division producing non-
identical daughter cells (1n)
Dr. J Moghraby
identical daughter cells (1n)
Both cell divisions go through interphase

11. Mitotic & Meiotic Cell Cycles
Mitosis
Dr. J Moghraby
Meiosis
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

12. Interphase
During all three phases the cell grows and carries out
metabolic activities
Organelles are produced
DNA is duplicated during S phase only;
Dr. J Moghraby
DNA is duplicated during S phase only;
chromosomes are dispersed in nucleus
Length of phases vary between cells

13. Mitosis
Generation of two identical daughter cells
from a single cell

14. Mitosis is Divided into Five Phases
Prophase
Prometaphase
Metaphase
Anaphase
Dr. J Moghraby
Anaphase
Telophase
Cytokinesis begins during telophase

15. Prophase
Chromosomes begin to condense
Mitotic spindle of microtubules begins to form
Nucleoli disappear and nuclear envelope begins to
break downbreak down
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

16. Prometaphase
Fragmentation of nuclear envelope
Mitotic spindle attach to the
condensed chromosomes at their
centromeres via kinetochores
Chromosomes have a bi-
orientaion
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

17. Metaphase
Kinetochores and spindle fibres
align the chromosomes at the
metaphase platemetaphase plate
Checkpoint determines whether
spindles are assembled properly
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

18. Anaphase
Sister chromatids separate
Kinetochore microtubules shorten
pulling the chromosomes topulling the chromosomes to
opposite spindle poles
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

19. Telophase & Cytokinesis
Chromosomes reach poles; begin to expand
Microtubules are lost
Nuclear envelope reforms
Cytokinesis results in two genetically identical
daughter cellsdaughter cells
Dr. J Moghraby
Cleavage furrow
100 m
Daughter cells
Cleavage of an animal cell (SEM)
Contractile ring of
microfilaments
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

20. MITOTIC (M) PHASE
Cytokinesis
Mitosis
SG1
G2
Mitotic Division
Dr. J Moghraby
Telophase &
Cytokinesis
Anaphase
Metaphase
Prometaphase
Prophase

21. Meiosis
Generation of four, genetically distinct,
haploid cells from a single cell

22. Meioun from Greek meaning ‘to make small’
Restricted to germ cells in gonads
Gametes have a haploid set of 23 chromosomes
Male = sperm
Dr. J Moghraby
Male = sperm
Female = ova

23. Timing of Meiosis Differs
Spermatogonia enter meiosis at different times (after
puberty)
Oogonia enter meiosis within fetal ovary arresting at
meiosis I prophase; oocytesmeiosis I prophase; oocytes
Oocytes re-enter meiosis when ovulated in response
to hormones
Dr. J Moghraby

24. Meiosis Consists of Two Divisions
Meiosis I: homologous chromosomes separate to
produce two haploid cells; reductional division
Meiosis II: sister chromatids separate resulting in four
haploid cells; equational division
Dr. J Moghraby
haploid cells; equational division
DNA duplication occurs before meiosis I in interphase

25. Stages of Meiosis
Interphase
Homologous pair of chromosomes
in diploid parent cell
Dr. J Moghraby
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids Diploid cell with
replicated
chromosomes

26. Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Dr. J Moghraby
Sister
chromatids Diploid cell with
replicated
chromosomes
Meiosis I
Homologous
chromosomes
separate
1
Haploid cells with
replicated chromosomes

27. Interphase
Homologous pair of chromosomes
in diploid parent cell
Chromosomes
replicate
Homologous pair of replicated chromosomes
Sister
chromatids Diploid cell with
replicated
chromosomes
Dr. J Moghraby
chromosomes
Meiosis I
Homologous
chromosomes
separate
1
Haploid cells with
replicated chromosomes
Meiosis II
2 Sister chromatids
separate
Haploid cells with unreplicated chromosomes

28. Meiosis I
Prophase I
Metaphase I
Anaphase I
Meiosis II
Prophase II
Metaphase II
Anaphase IIAnaphase I
Telophase I &
cytokinesis
Anaphase II
Telophase II &
cytokinesis
Dr. J Moghraby

29. Meiosis I
Prophase I:
– Takes up ~90% of time of meiosis
– Chromosomes condense
– Formation of tetrad
– Crossing over between homologous chromatids in regions– Crossing over between homologous chromatids in regions
called chiasmata
Dr. J Moghraby© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

30. Metaphase I:
– Pairs of homologous chromosomes
line up on metaphase plate opposite
each other
– Kinetochores on sister chromatids
face same pole
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

31. Anaphase I:
– Homologous chromosomes
move to opposite poles;
sister chromatids stay
attachedattached
Telophase I & Cytokinesis:
– Cell divides to produce two
haploid cells with two
attached sister chromatids
Dr. J Moghraby
Anaphase I Telophase I &
Cytokinesis
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

32. Meiosis II
Enter without going through interphase or replicating
DNA
Similar to mitosis but with only half number of
chromosomeschromosomes
Dr. J Moghraby

33. Prophase II:
– Spindle formation and
condensation of chromosomecondensation of chromosome
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

34. Metaphase II:
– Sister chromatids arranged on
metaphase platesmetaphase plates
– Kinetochores attach to
microtubules extending from
opposite poles
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

35. Anaphase I:
– Sister chromatids separate, and
move towards opposite poles ofmove towards opposite poles of
the cell
– Due to crossing over, sister
chromatids are no longer
identical
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

36. Telophase II & Cytokinesis:
– Nuclei form, cell divides to
produce two haploid cellsproduce two haploid cells
– Cytokinesis separates the
cytoplasm
– Result is four haploid cells
containing a single copy of
each chromosome
Dr. J Moghraby
© 2008 Sinauer Associates Sadava, D. et al. Life: The Science of Biology, 8th ed.

37. Number of viable gametes from meiosis differs
In males, meiosis results in four spermatids of similar
size
In females, meiosis is asymmetric; only one oocyteIn females, meiosis is asymmetric; only one oocyte
produced
Dr. J Moghraby BIOL101

38. Meiotic Timelines for Humans
Dr. J Moghraby
© 2001 Nature Publishing Group Hassold, T. & Hunt, P.

39. Meiotic Division
Metaphase IProphase I Anaphase I
Telophase I and
Cytokinesis
Dr. J Moghraby
Prophase II Metaphase II Anaphase II
Telophase II and
Cytokinesis

40. Comparison of Mitosis and Meiosis in
Diploid Cells
MITOSIS MEIOSIS
MEIOSIS I
Prophase I
Chiasma
Chromosome
replication
Homologous
chromosome
pair
Chromosome
replication
2n = 6
Parent cell
Prophase
Replicated chromosome
Dr. J Moghraby
Metaphase Metaphase I
Anaphase I
Telophase I
Haploid
n = 3
Daughter
cells of
meiosis I
MEIOSIS II
Daughter cells of meiosis II
nnnn
2n2n
Daughter cells
of mitosis
Anaphase
Telophase

41. Summary
Cell cycle consists of interphase followed by M-phase
Three major checkpoints regulate cell cycle
Mitosis results in two genetically identical daughter
cells from a single cell
Meiosis results in four, haploid daughter cells that are
Dr. J Moghraby BIOL101
Meiosis results in four, haploid daughter cells that are
genetically distinct