1. Mitosis and Meiosis Notes

2. Organisms can reproduce sexually or asexually
Asexual Reproduction
Single parent passes all genes to offspring
Identical “clones” of parent
Entire population of species is identical
Common in unicellular organisms

3. This sea star is regenerating a lost arm
Some organisms can also reproduce asexually
This sea star is regenerating a lost arm
Regeneration results from repeated cell divisions

4. Sexual Reproduction
Unique combination of 2 parents genes; each contributing half the offspring’s DNA
Combination of parental genes and traits
Wide variation in physical and behavioral traits
Common in multicellular organisms

5. What is a prokaryotic cell?
A little bit of review…
What is a prokaryotic cell?
A. a cell without a nucleus
B. a cell with a nucleus
C. I’m pretty sure I never heard that word.

6. PROKARYOTIC CELLS DIVIDE ASEXUALLY
These cells possess a single chromosome, containing genes
The chromosome is replicated
The cell then divides into two cells, a process called binary fission
Prokaryotic chromosomes
Figure 8.3B

7. Binary fission of a prokaryotic cell
Plasma membrane
Prokaryotic chromosome
Cell wall
Duplication of chromosome and separation of copies
Continued growth of the cell and movement of copies
Division into two cells
Figure 8.3A

8. A little bit more review…
You are made up of Eukaryotic cells.
A. True
B. False

9. THE EUKARYOTIC CELL CYCLE AND MITOSIS
A eukaryotic cell has many more genes than a prokaryotic cell
The genes are grouped into multiple chromosomes, found in the nucleus
The chromosomes of this plant cell are stained dark purple
Figure 8.4A

10. Chromosome distribution to daughter cells
Chromosomes contain a very long DNA molecule with thousands of genes
Individual chromosomes are only visible during cell division
Before a cell starts dividing, the chromosomes are duplicated
This process produces sister chromatids
Chromosome duplication
Sister chromatids
Centromere
Chromosome distribution to daughter cells

11. Why do we need more cells?
What IS Mitosis?
A way for the cell to make an EXACT copy of itself.
Each daughter cell has EXACTLY the same DNA as the original cell.
In humans, the original cell starts with 46 chromosomes, and ends with 46 chromosomes.
Why do we need more cells?
To GROW bigger in size
To REPLACE old, worn out cells
To REPAIR injuries
To REPRODUCE for some unicellular organisms

12. MITOSIS The cell cycle consists of two major phases:
Interphase, where DNA makes a copy of itself and organelles are made.
Mitosis: when cell division occurs
Figure 8.5

13. *DNA exists as chromatin. *Growth and DNA Replication occur
INTERPHASE
PROPHASE
Centrosomes (with centriole pairs)
Fragments of nuclear envelope
Chromatin
Spindle microtubules
Nucleolus
Nuclear envelope
Plasma membrane
*DNA exists as chromatin.
*Growth and DNA Replication occur
*90% of a cell’s life cycle is in this
stage
*Chromatin condenses to
chromosomes.
*Spindle fibers form.
*Nuclear envelope breaks up and the
centrioles align at the poles.

14. TELOPHASE AND CYTOKINESIS
METAPHASE
ANAPHASE
TELOPHASE AND CYTOKINESIS
Cleavage furrow
Nucleolus forming
Metaphase plate
Nuclear envelope forming
Spindle
Daughter chromosomes
*Chromosomes line up single file in the middle of the cell, perpendicular to the centrioles.
*Spindle fibers are attached to the centromeres.
*Spindle fibers retract, ripping the chromosomes in half at the centromere. *Identical chromosomes are pulled to the poles of each side of the cell.
*Chromosomes become chromatin. *Nuclear envelope reforms, cleavage furrow develops in animal cells and the cell eventually splits.

15. CYTOKINESIS This process pinches the cell apart Cleavage furrow
Contracting ring of microfilaments
Daughter cells

16. Mitosis Animation
Another Mitosis Animation

17. Review of the functions of mitosis:
Growth (seen here in an onion root)

18. Cell replacement (seen here in skin)
Dead cells
Epidermis, the outer layer of the skin
Dividing cells
Dermis

19. Asexual reproduction (seen here in a hydra)

20. A Review of Sexual Reproduction:
Unique combination of 2 parents genes; each contributing half the offspring’s DNA
Combination of parental genes and traits
Wide variation in physical and behavioral traits
Common in multicellular organisms

21. You are a combination of two gametes (or sex cells)
Cells with two sets of chromosomes (like your body cells) are said to be diploid (humans = 46)
Gametes are haploid, with only one set of chromosomes (humans = 23)
= 46

22. At fertilization, a sperm fuses with an egg, forming a diploid zygote
Mitosis continues throughout the life cycle.
The adult makes haploid gametes by MEIOSIS

23. Multicellular diploid adults (2n = 46) Mitosis and development
So, what is MEIOSIS?
The creation of sperm and eggs
Haploid gametes (n = 23)
Egg cell
Sperm cell
MEIOSIS
FERTILIZATION
Diploid zygote (2n = 46)
Multicellular diploid adults (2n = 46)
Mitosis and development

24. MEIOSIS I: Homologous chromosomes separate
Interphase: Growth and DNA Replication occur. DNA exists as chromatin. Most of a cell’s life cycle is in this stage.
Prophase I: Chromatin coils up into chromosomes. Homologous chromosomes, composed of sister chromatids, come together as pairs. The nuclear envelope breaks up. Spindle fibers form.
INTERPHASE
PROPHASE I
METAPHASE I
ANAPHASE I
Centrioles)
Nuclear envelope
Chromatin

25. Metaphase I: The chromosome pairs line up between the poles
Metaphase I: The chromosome pairs line up between the poles. Spindle fibers are attached at the centromere. Crossing over may occur.
Anaphase I: Chromosome pairs are separated and double chromosomes move to opposite poles toward the centrioles.
Telophase I: Cleavage furrow develops, nuclear envelope begins to reform. Double chromosomes start to uncoil. Eventually, the cell splits into two.

26. TELOPHASE II AND CYTOKINESIS
MEIOSIS II
Prophase II: Spindle fibers form, nuclear envelope breaks up. Chromatin coils up into double chromosomes (composed of sister chromatids).
Metaphase II: Double chromosomes line up single file in the center of the cell. Spindle fibers are attached at the centromere.
TELOPHASE II AND CYTOKINESIS

27. Anaphase II: Spindle fibers retract, ripping the double chromosomes in half at the centromere. Single chromosomes are pulled to the poles of each side of the cell.
Telophase II: Nuclear envelope reforms, chromosomes uncoil into chromatin. Cleavage furrow develops in both cells and eventually splits into 4 sex cells, each with the haploid number of chromosomes.

28. MEIOSIS is different in BOYS and GIRLS
SPERMATOGENESIS
OOGENESIS
*Made in the testes
*Made in the ovaries

29. Meiosis Animation
Comparison of mitosis & meiosis animation