This is a Lesson about the Mitosis and Meiosis for General Biology 1

1. The Cell Cycle

2. The Cell Cycle
 The sequence of
growth and division of a
cell

4. 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)

5. 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.

6. MITOSIS
 The process by which the cell nucleus divides
into two identical cell nuclei.
 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
 Structures of the tightly packaged
DNA
 Must duplicate and separate
during Mitosis
 DNA is tangled up into a substance
of chromatin
 The chromatin is packaged on the
chromosome

8. Chromosomal structure

9. 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.

10. Prophase

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. 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.

14. Anaphase

15. 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.

16. Telophase

17. CYTOKINESIS
The two identical cells
completely divide and
the cell membrane is
completely formed.

18. 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.

19. HAPLOID CELLS
 Haploid cells are called gametes
 Gametes are either sper'm or eggs
 Organism diploid gamete
Human 46 23
Pea 14 7
Fruit fly 8 4
Dog 78 39

20. 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.

21. 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.

22. 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.

23. 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

24. METAPHASE I
 Homologous chromosomes
line up together in pairs.
* In mitosis homologous
chromosomes line up in the
middle independently of
each other.

25. 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.

26. 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.

27. Meiosis I

28. 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

29. 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.

30. Meiosis II

31. Malfunction
During
Cell Cycle