Presentation discusses the cell cycle of somatic and sex cells

1. The Cell Cycle-
Mitosis and Meiosis
Interphase- G1, S, G2
Mitosis or Meiosis

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
 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. 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. Phase
Chromosome
Appearance & Location
Important Events
Interphase
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
DNA replication, cell
grows and replicates
organelles
Nuclear envelope
disappears, spindle fibers
form
DNA copies itself;
chromatin
Chromosomes coil up
Chromosomes line up in
the middle
Spindle fibers connect to
chromosomes
Chromosome copies divide
and move apart
Spindle fibers pull
chromosome copies apart
to opposite poles
Chromosomes uncoil back
into chromatin
Nuclear envelopes reform,
2 new nuclei are formed,
spindle fibers disappear
Division of the rest of the
cell: cytoplasm and
organelles
Chromatin

19. 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.

20. 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

21. 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.

22. 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.

23. Image: Meiosis diagram, Marek Kultys
From the Virtual Cell Biology Classroom on ScienceProfOnline.com

24. 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.

25. 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

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

27. 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.

28. 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.

29. Meiosis I

30. 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

31. 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.

32. Meiosis II