Mitosis and Meiosis

1. University of Duhok
College of Health Sciences
Dep. of Medical Laboratories
Biology/1st Stage
Lecture 5
Dr.: Shameeran S. Ismael
BVM & S, M.Sc Medical Microbiology(Parasitology),
PhD Molecular Parasitology

2. Cell Division in Eukaryotes

3. I.Mitosis
• The process of cell nucleus division which results
in the production of two identical daughter cells
from a single parent cell.
• The daughter cells are identical to one another and
to the original parent cell
.

4. Mitosis vs. Meiosis
Mitosis: is a division of the nucleus
Meiosis: is a making of haploid gametes
• Mitosis involves ONE nuclear division
• Meiosis involves TWO nuclear divisions

5. Why does Mitosis occur?
• When cells get too big they can no longer get
enough nutrients through the cell membrane in order
to maintain it’s entire self.
• In other words it does not have enough surface area
to diffuse in enough nutrients or diffuse out all
wastes.

6. Mitosis can be explained in Phases
• Regular cell activity and Mitosis can be
explained in 5 basic phases including:
1. Interphase
2. Prophase
3. Metaphase
4. Anaphase
5. Telophase.

7. 1.Interphase
• The cell prepares for
division
• DNA replicated
• Organelles replicated
• Cell increases in size
Chromatin
Interphase – In Between

8. 2.Prophase
•DNA get small and condenses into chromosomes
• Nuclear membrane breaks down and nucleus
disappear
• Centrioles move to the poles of the nucleus and
spindle fibers develop
Prophase - “Preparing’’

9. 3.Metaphase
• The cell prepares chromosomes for
division
• Chromosomes line up at the center of
the cell
• Spindle fibers attach from daughter
cells to chromosomes at the centromere
Metaphase –
“Middle”
Pole
Equator

10. 4.Anaphase
• The chromosomes divide
• Spindle fibers pull
chromosomes apart
• ½ of each chromosome
(called chromotid) moves to
each daughter cell
Anaphase –
“Away” or “Apart”

11. 5.Telophase
• Chromosomes reach opposite ends of
the cell
• Spindle fibers disassemble
• Chromosomes unravel
• Cytoplasm divides in two
• Nuclear membranes reform
Telophase – “Two”

12. II. Meiosis
• Meiosis is the process of cell division in which
gametes are formed and the number of
chromosomes is halved. So that sexual reproduction
and zygote formation can occur.
• Zygote: Fertilized egg which has a diploid number
of chromosomes.
• During meiosis, DNA replicates once, but the
nucleus divides twice

13. Stages of Meiosis
1. Interphase:
– Chromosomes replicate
– Each chromosome consists of 2 identical sister
chromatids
2.Prophase I
– Each chromosome duplicates and remains closely
associated. These are called sister chromatids.

14. 3.Metaphase I:Chromosomes align at the center of
the cell
4. Anaphase 1: Chromosome pairs separate with
sister chromatids remaining together.
5.Telophase 1: Two daughter cells are formed with
each daughter containing only one chromosome of
the chromosome pair.

15. Meiosis II
• Is basically just like mitosis, but remember the
chromosomes did not duplicate in interphase II.
1.Prophase 2: DNA does not replicate.
2. Metaphase 2: Chromosomes line up at the
center of the cell
3. Anaphase 2: Centromeres divide and sister
chromatids move separately to each pole

16. 4. Telophase 2:
• Cell division is complete.
• Four haploid daughter cells are formed.

18. Products of Mitosis & Meiosis
• Mitosis produces two identical daughter cells
• Meiosis produces four genetically different
daughter cells

19. The Numbers
• The cells from mitosis are diploid or 2n.
• The cells from meiosis are haploid or n.
Definitions:
• Diploid (2n) – full set of chromosomes
• Haploid (n) – half set of chromosomes

20. Haploid vs Diploid
• The diploid number (2n) in humans is 46.
• The haploid number (n) in humans is 23.
• Example: The diploid number in a horse is 64.
What is the haploid number?
• Example: The haploid number in cats is 19.
What is the diploid number?

21. Where do these processes occur?
• Mitosis occurs in somatic cells (body cells)
like heart cells, skin cells, etc
• Meiosis occurs in sex cells (gametes) like
sperm & egg cells only.

23. The reason why: mitosis
• To replace damaged cells
• To allow for growth & development
• To prevent cells from getting too big
• For asexual reproduction

24. The reason why: meiosis
• To create gametes that can combine to make a
zygote
• For sexual reproduction
• To increase genetic diversity (crossing over,
independent assortment, random fertilization)

25. Mitosis VS. Meiosis
Mitosis
• Asexual
• Cell divides once
• Two daughter cells
• Genetic information
is identical
Meiosis
•Sexual
•Cell divides twice
• Four haploid daughter
cells
• Genetic information is
different

26. Mitosis vs. Meiosis

27. Spermatogenesis
• Occurs in the testes
• Two divisions produce 4 spermatids
• Spermatids mature into sperm
• Men produce about 250,000,000 sperm per day

28. Spermatogenesis

29. Oogenesis
• Occurs in the ovaries
• Two divisions produce 3 polar bodies and 1
egg
• Polar bodies will die because of unequal
division of cytoplasm
• Immature egg called oocyst
• Starting at puberty, one oocyst mature into an
ovum (egg) every 28 day

30. Oogenesis

31. Thanks for attention,,,