1. Cell Reproduction
Part 1: Chromosomes

2. Cells All living things are made up of one or more cells.
These cells all contain DNA (deoxyribonucleic acid) which is your genetic material.
DNA can be stored in two forms as either chromatin (relaxed or unraveled) or as chromosomes (coiled)

3. DNA Chromatin coils to form a chromosome.
Chromosomes are rod shaped and comprised of both DNA and proteins called histones.
Histones are proteins that help the DNA maintain the coiled shape of a chromosome.
DNA needs to be relaxed in order to be read. However, it is never completely uncoiled as it would take up too much space. And it is never super coiled into a chromosome unless a cell is dividing.

4. Chromosome Structure
Most of the time, your cells are not dividing. Therefore you have unduplicated chromosomes.
A dividing cell will have a duplicated chromosome which is made up of identical chromatids
Constricted area is the centromere
This is a eukaryotic chromosome. Prokaryotic organisms only have one chromosome and it is round.

5. Chromosome Structure (continued)
What kind of chromosome is this?
Chromosomes contain genes which are areas of DNA that code for particular proteins.

6. Types of Chromosomes and Numbers
There are two types
Sex Chromosomes: determine the sex (gender) of an organism
Autosomes: does not determine gender
Every cell has two copies of each autosome – 1 from mother and 1 from father called homologous chromosomes or homologues
Homologous chromosomes carry the same type of genetic information but it may not be identical
Every cell has 2 sex chromosomes that can differ depending on what they receive from their parents
XX – female
XY – male
Does the number of chromosomes have anything to do with the complexity of an organism?

7. Karyotypes Photomicrograph of the chromosomes in a dividing cell
Human karyotypes show 22 homologous pairs of autosomes and 2 sex chromosomes
What do you notice about the arrangement?
Is this a male or female?

8. Diploid and Haploid Cells
Diploid (di=2) cells have two sets of chromosomes
All normal human cells (except reproductive) are diploid and called somatic (body) cell
Represented by 2n
Haploid (one) cells only have one set of chromosomes
All reproductive cells (sperm and egg); called gametes(sex cells)
Represented by 1n
A haploid cell has the possibility of joining together with another haploid cell to form a diploid cell. (fertilization)

9. Cell Reproduction
Part 2: Cell Cycle

10. Prokaryotic Division
Binary fission: division of a prokaryotic cell in two offspring cells
Three general stages
Copy DNA
Grow
Divide

11. Cell Division in Eukaryotes
Two types in eukaryotes
Mitosis
Results in two cells with genetic material identical to the original cell – used for: repair, growth, and asexual reproduction
Meiosis
Reduces the chromosome number by half and the genetic material is not the same
Produces gametes which are sex cells
Part of sexual reproduction
The gametes are haploid cells which retain the ability to join together and form diploid cells.

12. The Cell Cycle
Two major phases of the cell are interphase and cell division
Interphase is the time between divisions
Cell division is the division of the nucleus (mitosis) and the cytoplasm (cytokinesis)

13. Interphase Divided into three sub-phases G1: where the cell matures
S: DNA is replicated
G2: Cell prepares for division
*Cells do not divide forever*
G0: cells have exited the cell cycle and do not copy DNA or divide any more

14. Mitosis Division of the nucleus; called the M phase
It is divided into four different phases
Prophase
Metaphase
Anaphase
Telophase

15. Prophase Shortening and tightening of DNA into chromosomes
The nuclear membrane and nucleolus disappear
Centrosomes appear and migrate toward the poles of the cell. In animal cells, the centrosomes contain centrioles.
Spindle fibers begin to radiate form the centrosomes
Kinetochore fibers
Polar fibers

16. Metaphase
Chromosomes are easier to identify - can easily see the X shape.
Kinetochore fibers move the chromosomes to the center.
Once there the chromosomes are held in place. 14

17. Anaphase
The chromatids separate and move centromere first to opposite poles
Once the chromatids separate they are considered to be individual chromosomes 15

18. Telophase
Once the chromosomes reach the poles of the cell the spindle fibers disassemble
The chromosome returns to its uncoiled state
Nuclear membrane and a nucleolus forms in each cell

19. Cytokinesis During telophase the cytoplasm begins to divide Animals
Cleavage Furrow: pinching inward of the membrane midway of the poles
Plants
Cell Plate: Vesicles formed by the Golgi apparatus fuse midway of the dividing cell

20. End Result The end result of mitosis is two identical daughter cells.
The cells will go back to interphase to grow and develop into full cells.

21. Control of Cell Division
Cell growth (G1 ) checkpoint: the cell determines if it is ready to start the process of division
DNA synthesis (G2) checkpoint: check DNA synthesis
Mitosis checkpoint: check if mitosis proceeded correctly
When control is lost it can lead to cancer

22. Chapter 8 Part 3: Meiosis and Reproduction
Cell Reproduction
Chapter 8 Part 3: Meiosis and Reproduction

23. Meiosis
Meiosis
Reduces the chromosome number by half and the genetic material is not the same
Produces gametes which are sex cells
Part of sexual reproduction
The gametes are haploid cells which retain the ability to join together and form diploid cells.

24. Meiosis
Very similar to mitosis but produces haploid cells instead through 2 divisions: Meiosis I and Meiosis II
None of the cells have the same genetic information

25. Prophase I
All of the aspects of prophase that occur in mitosis occur here as well
Synapsis: pairing of homologous chromosomes
Tetrad: the pair formed in synapsis
Crossing-over: portions of the chromosomes break off and exchange with homologue
Genetic Recombination: new genetic material is made

26. Metaphase I and Anaphase I
The tetrads line up in the middle of the cell
Anaphase I
Here the homologous chromosomes separate and go toward opposite poles
Since they randomly lined up in metaphase, they now randomly separate. This process is called independent assortment.
Independent Assortment: the random separation of homologues

27. Telophase I and Cytokinesis I
Here the cell will split into two new cells
The end result is two cells that are haploid cells.
Each cell is now considered haploid cells, even though they have two copies of that chromosome. This is due to the fact that it no longer has a homologue.

28. Meiosis II Occurs on the two cells formed during meiosis I
Same procedure as mitosis
End result of meiosis II is four new cells containing half the number of chromosomes of the original cell
**Some cells will start meiosis after the nuclear membrane completely reforms; others start at the end of meiosis I 23

29. Nondisjunction Sometimes errors can occur in meiosis
Whether the homologous chromosomes fail to separate in anaphase I or the sister chromatids fail to separate in anaphase II, nondisjunction has occurred.
This will lead to one or more sex cells that have too many chromosomes and one or more sex cells that are missing a chromosome.
The result is a genetic disorder.

31. Specific Gamete Formation
Meiosis occurs only in the reproductive organs in animals
Spermatogenesis
Each haploid cell called a spermatid is form; spermatids develop into sperm cells
Oogenesis
In cytokinesis I and II the cytoplasm does not split evenly
One egg (ovum) developed and three polar bodies
The polar bodies will eventually degenerate

32. Asexual Reproduction Requires 1 parent - produces identical offspring
Types
Mitosis
Budding
Parthenogensis
Fragmentation
Benefits
Quick
Produce many offspring at one time
No energy wasted on finding a mate
Cons
No genetic variation – could lead to the extinction of a species.

33. Sexual Reproduction
Requires 2 parents – leads to genetically different offspring.
Benefits
Offspring are genetically different than each other and their parents*** - This allows a species to adapt to rapidly changing conditions.
Cons
Must find a mate
Expend energy in producing gametes that may not be fertilized
*** With the exception of identical twins!***