The document describes the cell cycle process of mitosis and meiosis. It explains that mitosis produces two identical daughter cells from one parent cell through the phases of interphase, prophase, metaphase, anaphase, telophase and cytokinesis. Meiosis produces four unique haploid daughter cells from one diploid parent cell through the two divisions of meiosis I and meiosis II, where homologous chromosomes separate then sister chromatids separate, respectively, reducing the chromosome number by half. The accurate transmission of chromosomes is essential for sexual reproduction and genetic variation.

1. Lesson 2: The Cell Cycle-
Mitosis and Meiosis
Mae Anne M. Villarosa, MASE
Instructor I ( Science)

2. The Cell Cycle
• The sequence of growth
and division of a cell
• Cell division both
happens in somatic cells
and sex cells.

3. Interphase = G1, S, G2
• Interphase is when the cell grows, and the
organelles double prior to the actual splitting of
the nucleus.
• 93% of a cell’s life is spent in interphase.
• Interphase has three parts
• Growth 1 (G1)
• Synthesis (S)
• Growth 2 (G2)

4. G1, S, G2
• G1 is when organelles double.
• Remember each new cell needs a complete set of
organelles.
• S when DNA is replicated.
• Each cell needs a complete and identical set of DNA
• G2 Proteins needed for Mitosis are produced.

5.  Division of somatic cells (non-reproductive cells) in
eukaryotic organisms.
 A single cell divides into two identical daughter cells.
 Daughter cells have same # of chromosomes as does parent
cell.
Mitosis
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Images: Cell cycle by Richard Wheeler;
Overview of Mitosis, Mysid

6. Mitosis
In some Human cells interphases lasts 15.3 hours,
while mitosis lasts only .7 hours.
Occurs in a series of steps
 Prophase
 Metaphase
 Anaphase
 Telophase
 Cytokinesis

7. Chromosomes
Must duplicate and separate
during Mitosis
Structures of the tightly packaged
DNA
DNA is tangled up into a
substance of chromatin
The chromatin is packaged on the
chromosome

8. Prophase
Chromosomes now called chromatids because they
doubled to form short thick rods which pair up and line
up in the center of the nucleus.
A centromere connects the two halves of the doubled
chromatids.
Spindle fibers begin to form.
 Spindle fiber – a fibrous structure from the cytoplasm which
forms to the centriole.
Centrioles move to opposite sides of the cell.
The nuclear membrane breaks down.

9. Prophase

10. Images: Prophase drawing, Henry Gray's Anatomy of the Human Body;
Prophase Onion Cell Drawing & Photo, Source Unknown, Fluoresced cell,
National Institutes of Health
3 Major Events
- chromosomes condense
- spindle fibers form
(spindle fibers are specialized microtubules
radiating out from centrioles)
- chromosomes are
captured by spindle
From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Fluoresced eukaryotic cell.
Chromosomes in blue. Mitotic spindle
apparatus in green.

11. Metaphase
Centromeres of the chromatid pairs line up in
the middle of the cell.
Metaphase plate- location where the
centromeres line up in the center of the cell.
By the end of metaphase each chromatid has
attached to spindle fibers.

12. Metaphase

13. • chromosomes align along
equator of the cell, with one
kinetochore facing each pole
centrioles
spindle fibers
chromosomes
Images: Metaphase drawing, Henry Gray's Anatomy of the Human
Body; Metaphase Onion Cell Drawing & Photo, Source Unknown
Kinetocores not pictured in this illustration.

14. Anaphase
The spindle fibers pull the chromatids apart.
This separates each one from its duplicate. These
move to opposite sides of the cell.
Now there are two identical sets of
chromosomes.

15. Anaphase

16. • sister chromatids separate
• spindle fibers attached to
kinetochores shorten and pull
chromatids towards the poles.
• free spindle fibers lengthen
and push the poles of the cell
apart
Images: Anaphase drawing, Henry Gray's Anatomy of the Human
Body; Anaphase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com

17. Telophase
• When the chromosomes reach opposite sides of
the cell the spindle fibers break up.
• The nuclear membrane begins to reform.
• A furrow begins to develop between the two sets
of chromosomes.

18. Telophase

19. • spindle fibers disintegrate
• nuclear envelopes form around both groups
of chromosomes
•chromosomes revert to their extended state
• cytokinesis occurs, enclosing each daughter
nucleus into a separate cell
Images: Telophase drawing, Henry Gray's Anatomy of the Human
Body; Telophase Onion Cell Drawing & Photo, Source Unknown From the Virtual Cell Biology Classroom on ScienceProfOnline.com

20. Cytokinesis
• The two identical cells completely divide and the cell
membrane is completely formed.
• Plant cells undergo cytokinesis by
forming a cell plate between the two
daughter nuclei.
• Animal cells undergo cytokinesis
through the formation of a cleavage
furrow. A ring of microtubules
contract, pinching the cell in half.

21. Image: Onion Cell Drawing & Photo, Source Unknown

22. Image: Superficial human anatomy, Mikael Häggström&
Rainer Zenz; Sperm & egg, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com

23. - A single germ cell divides into four unique daughter cells.
- Daughter cells have half the # of chromosomes as parent
cell, so they considered haploid.
Image: Overview of Meiosis,
National Institutes of Health From the Virtual Cell Biology Classroom on ScienceProfOnline.com
Meiosis

24. Meiosis
Diploid (2n) - A cell with two of each kind of
chromosome.
One chromosome from each parent.
If two body cells were to combine nuclei, the
number of chromosomes would double.
In order for sexual reproduction to occur, each cell
involved must reduce its chromosome number by
half.
Haploid (n)- A cell with one of each kind of
chromosome.

25. Haploid cells
Haploid cells are called gametes
Gametes are either sperm or eggs
Organism Diploid Gamete
Human 46 23
Pea 14 7
Fruit fly 8 4
Dog 78 39

26. Homologous chromosomes
Are paired chromosomes with genes for the
same trait arranged in the same order.
ex. Eye color, hair color, height, one may code for
blue, blonde, tall, its homolog may code for brown,
blonde, short
Homologous chromosomes may have different
alleles on them
Allele- gene form for each variation of a trait of
an organism.

27. 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.

28. Diploid organisms receive one of each type of
chromosome from female parent (maternal chromosomes) and
one of each type of chromosome from male parent
(paternal chromosomes)
Refers to the number of sets of
chromosomes in cells.
● Haploid – one copy of each chromosome
– designated as “n”, the number of
chromosomes in one “set”
- gametes
● Diploid – two sets of chromosomes
- two of each chromosome
– designated as “2n”
- somatic cells
Genetics Terminology: Ploidy
From the Virtual Cell Biology Classroom on ScienceProfOnline.com

29. Genetics Terminology: Homologues
Chromosomes exist in homologous pairs in
diploid (2n) cells.
Exception: Sex chromosomes (X, Y).
Other chromosomes, known as autosomes, they have homologues.
From the Virtual Cell Biology Classroom on ScienceProfOnline.com

30. Karyotype
•Q: Which, of the top
two karyotypes is
replicated?
•Q: How many
homologous pair in
each karyotype?
•Q: How is the bottom
karyotype different
from the top two?

31. Asexual Reproduction
•Many single-celled organisms
reproduce by splitting,
budding.
•Some multicellular organisms
can reproduce asexually,
produce clones (offspring
genetically identical to parent).
•Q: What type of cell division is
asexual reproduction?
Image: Paatrick Star, Nickelodeon;
Hydra budding, Lifetrance;
From the Virtual Cell Biology Classroom on ScienceProfOnline.com

32. Sexual Reproduction
•Fusion of two gametes to
produce a single zygote.
•Introduces greater genetic
variation, allows genetic
recombination.
•With exception of self-fertilizing
organisms, zygote has gametes
from two different parents. Peter + Lois = Stewie
Images: Peter, Lois & Stewie, The Family Guy From the Virtual Cell Biology Classroom on ScienceProfOnline.com

33. Sexual reproduction in humans …
• At fertilization, 23 chromosomes
are donated by each parent.
(total = 46 or 23 pairs).
• Gametes (sperm/ova):
• Contain 22 autosomes and 1 sex
chromosome.
• Are haploid (haploid number
“n” = 23 in humans).
• Fertilization results in diploid zygote.
• Diploid cell; 2n = 46. (n = 23 in humans)
Q: Most cells in the body are produced through what type of
cell division?
• Only gametes are produced through meiosis.
Image: Superficial human anatomy, Mikael
Häggström& Rainer Zenz; Sperm & egg, Wikipedia From the Virtual Cell Biology Classroom on ScienceProfOnline.com

34. Stages of Meiosis
•Interphase-
• Chromosomes replicate
• Each chromosome consists of 2 identical sister
chromatids
•Prophase I
• Each Pair of homologous chromosomes come
together to form a tetrad.
• Tetrad- 2 homologous chromosomes come together
and the 4 chromatids overlap.

35. Crossing over
Tetrads are so tight that non-sister chromatids
from the homologous pair actually exchange genetic
material.
• Crossing over- The exchange of genetic material by
non-sister chromatids during late prophase I of
meiosis.
• Results in a new combination of alleles

36. Metaphase I
•Homologous chromosomes line up together in
pairs.
 In mitosis, homologous chromosomes line up in
the middle independently.

37. Anaphase I
•Spindle fibers attach to the centromeres of each
pair.
•Homologous chromosomes separate and move to
opposite ends of the cell.
•Centromeres DO NOT split like they do in
mitosis.
•Now, each cell will get one chromosome from
each homologous pair.

38. Telophase I
•Spindle fibers break down
• Chromosomes uncoil
• Cytoplasm divides
• Another cell division is needed because the
number of chromosomes has not been reduced
•After telophase I there maybe a short interphase,
but not always. It is important to note that if a
cell does have a second interphase, there is No
replication of chromosomes.

39. MEIOSIS I

40. Meiosis II
Is basically just like mitosis, but remember the
chromosomes did not duplicate in interphase II.
Prophase II
• Chromosomes begin to line up in the middle of the
cell.
• Spindle fibers begin to form
Metaphase II
Chromosomes line up on the metaphase plate

41. Meiosis II
Anaphase II
• Centromeres split
• Sister chromatids separate and move to opposite sides of the
cell
Telophase II
• Nuclei reform
• Spindle fibers disappear
• Cytoplasm divides into two.
The number of chromosomes in each daughter cell has
now been reduced by half.

42. MEIOSIS II

43. THANK YOU!!!