The document summarizes the cell cycle, including the stages of interphase (G1, S, G2), mitosis, and meiosis. It explains that the cell cycle involves cell growth and DNA replication in interphase, followed by nuclear division in mitosis. Meiosis involves two nuclear divisions to produce haploid gametes from a diploid cell, reducing the chromosome number by half to maintain genetic variation between generations.

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