1. The Processes of Cell Division --- Mitosis and Meiosis
Reproduction of Cells
The Processes of Cell Division ---
Mitosis and Meiosis

2. Cell Size Review…
What are some of the difficulties a cell faces as it increases in size?

3. Cell Size Review…
The larger a cell becomes, the more demands the cell places on its DNA. In addition, a larger cell is less efficient in moving nutrients and waste materials across its cell membrane.

4. Cell Size and Limits Living cells store critical information in DNA.
As a cell grows, that information is used to build the molecules needed for cell growth.

5. Cell Division
In order for cells to survive, they must constantly exchange ions, gases, nutrients, and wastes with their environment. These exchanges take place at the cell’s surface. To perform this function efficiently, there must be an adequate ratio between the cell’s volume and its surface area. As a cell’s volume increases, its surface area increases, but at a decreased rate. If you continued to increase the cell’s volume, it would soon be unable to efficiently exchange materials and the cell would die.

6. Compensation For Cell Size Limitations
Before a cell grows too large, it divides into two new “daughter” cells in a process called cell division.
Before cell division, the cell copies all of its DNA.

7. Reproduction of Cells Section 1 Chromosomes
Section 2 Cell Division & Mitosis
Section 3 Meiosis
Online interactive tutorial for additional materials:

8. By the Time We Finish This Segment …
Describe the structure of a chromosome. Identify the differences in structure between prokaryotic chromosomes and eukaryotic chromosomes. Describe the events of cell division in prokaryotes. Compare the numbers of chromosomes in different species. Explain the differences between sex chromosomes and autosomes. Distinguish between diploid and haploid cells.

9. Chromosomes - Made of DNA + Protein
Eukaryotes
DNA wrapped around proteins called histones.
Chromosomes are linear strands
Prokaryotes
Simpler in structure than eukaryotes.
Chromosomes are circular

10. Structure of a Chromosome

11. Basic Terms
Chromosomes - the double helix (double strand of 2 sugar-phosphate backbones) and are tightly coiled up.
Chromatid - Pairing with another chromosome to form two sister chromatids.
Centromere – “button” that holds chromosomes together.
Chromatin (DNA+histones) - is the loose form of chromosomes seen during interphase.

12. Anatomy of a Chromosome

13. Chromatin - Interphase

14. Rate of Cell Division – Which takes less time??
Prokaryotes
Binary Fission - the process of cell division in prokaryotes.
Eukaryotes
Mitosis - nuclear division producing two identical daughter cells

15. What is the difference between binary fission and mitosis?
Is NOT a form of asexual reproduction
IS a form of cellular reproduction that produces new cells for growth, repair, and the general replacement of older cells
Binary fission …
Is a form of asexual reproduction of an organism (single-celled)

16. Chromosome Numbers
Each species has a characteristic number of chromosomes in each cell.

17. Chromosome Numbers, continued
Autosomes and Sex Chromosomes
Chromosomes in an organism that are responsible for making body cells = autosomes. (2n) = diploid
Skin, Muscle, Hair, Kidney, Blood, etc.
Sex chromosomes are chromosomes that determine the sex of an organism. (1n) = haploid
Humans have 23 PAIRS chromosomes, but 46 total chromosomes

18. Chromosome Numbers, continued
Diploid and Haploid Cells
Cells having two sets of chromosomes are diploid (2n). (Also known as somatic cells)
Most all cells in our body
Haploid cells (1n) have only one set of chromosomes. (Also known as gametes)
Sex cells
1 comes from mom and 1 comes from dad

19. Karyotype
Karyotype – an organized profile of one’s chromosomes.

20. Mitosis (Cell division in eukaryotes)
Cellular division that produces 2 identical cells
Somatic cells

21. By the Time We Finish This Segment …
Name the two parts of the cell that are equally divided during cell division in eukaryotes.
Summarize the events of interphase.
Describe the stages of mitosis.
Compare cytokinesis in animal cells with cytokinesis in plant cells.
Explain how cell division is controlled.

22. Cell Division in Eukaryotes
Cell Cycle
The cell cycle is the repeating set of events in the life of a cell.
The cell cycle includes cell division and interphase.
Cell division in eukaryotes includes nuclear division, called mitosis, and the division of cytoplasm, called cytokinesis.
THESE ARE ALL KINDS OF CELLS (somatic, diploid) EXCEPT…Sex CELLS!!!

23. Reminder …. Types Of Cells and How They Divide
Somatic cells = All cells EXCEPT sex cells
Hair, Skin, Liver, Blood, etc.
Go through the process of MITOSIS
Sex cells (gametes) = Go through the process of MEIOSIS!

24. Cell Division – Trick to help remember…
I Pray More At The Church
Interphase – loooonnnngggg Intermission = longest stage of (NOT CONSIDERED PART OF MITOSIS!!!!)
G1 (growth), S (synthesis), G2 (prep for ÷)
G0 – can occur after G1, exiting the cell cycle; as is

25. Cell Division in Eukaryotes, continued
Interphase
Interphase consists of growth (G1), DNA replication (S), and preparation for mitosis (G2)

26. Mitosis: Nuclear division occurs (P, M, A, T)
Somatic cell Division Somatic cells (body cells) divide for the purpose of growth, replacement, and repair of damage cells or tissues.
Interphase: Preparation = DNA replicates, chemicals and organelle synthesis occurs.
Mitosis: Nuclear division occurs (P, M, A, T)
Cytokinesis: Division of the cytoplasm occurs, forming 2 genetically similar diploid cells

27. Cell Division - Steps of Mitosis
Back to: (I) Pray More At The Church
Prophase – the beginning of the PROduction as DNA forms into rod-shaped chromosomes
Sidebar notes: the 2 copies of the chromatids have occurred (S phase), and remain connected to each other by the centromere
As the centromeres separate, spindle fibers (microtubules – cell organelles chapter) radiate from the centromeres) … What macromolecule makes microtubules????

28. Cell Division – Steps of Mitosis
Continuing…. I Pray More At The Church
Metaphase – chromosomes line up in the Middle
Anaphase – pull Away from and go to either side of the cell
Telophase – chromosomes return to a less Tightly coiled chromatin state with nuclear envelops and a nucleolus around each of the new cells
AT THIS POINT, the nucleus has split into 2, BUT NOT the cell itself…. Yet.

29. Stages of Mitosis
Notice that when the chromosomes separate = single chromosomes

30. Cell Division – Cytokinesis
Continuing…. I Pray More At The Church
- Cytokinesis – Cell Splits in the Center, resulting in 2 – 2n (diploid – non-sex) cells

31. Cell Division - Cytokinesis
During cytokinesis in animal cells, a cleavage furrow pinches in and eventually separates the dividing cell into two cells.
In plant cells, a cell plate separates the dividing cell into two cells.

32. Control of Cell Division
Cell division in eukaryotes is controlled by many proteins.
Control occurs at three main checkpoints.
G1 (growth), S (synthesis), G2 (prep for ÷)

33. Control of Cell Division, continued
When Control is Lost: Cancer
Proteins that regulate cell growth are controlled by genes
If mutations occur with the genes, protein function is affected, resulting in disruption of cell growth and division
This disruption = uncontrolled growth of cells = Cancer

34. Control of Cell Division, continued
When Control is Lost: Cancer
An individual’s propensity for developing cancer depends on many factors
Family genetics
Exposure of carcinogens = cancer-causing agents
Genetic mutations (mutagens) that can occur from exposure to carcinogens

35. MEIOSIS (Cell division of sex cells) Gametes

36. By the Time We Finish This Segment …
Compare the end products of meiosis with those of mitosis.
Summarize the events of meiosis I.
Explain crossing-over and how it contributes to the production of unique individuals.
Summarize the events of meiosis II.
Compare spermatogenesis and oogenesis.
Define sexual reproduction

37. Formation of Haploid Cells (Sex cells)
Meiosis - a process of nuclear division that reduces the number of chromosomes in new cells to half the number in the original cell.
Meiosis leads to four haploid cells (gametes) rather than two diploid cells as in mitosis.
Meiosis occurs ONLY with sex cells ---- All other cells
are called somatic cells

38. Formation of Haploid Cells (Sex cells)
In order to finish cell division of haploid cells with the correct number of chromosomes… (steps of mitosis x 2)
Meiosis I and Meiosis II must occur
Meiosis I includes prophase I, metaphase I, anaphase I, and telophase I.
Results in DOUBLE the number of chromosomes needed for haploid cells to successfully exist and function in cell division.
Therefore, Meiosis II must occur to complete the process resulting in 4 HAPLOID cells

39. Stages of Meiosis – Notice split = TETRADS (2 Pair of Chromosomes)

40. Stages of Meiosis – Notice split = TETRADS (2 Pair of Chromosomes), continued

41. Formation of Haploid Cells (Sex cells)
During Prophase I of Meiosis:
Crossing-over = when portions of homologous chromosomes (single strand of a pair of chromosomes) exchange genetic material, occurs during prophase I and results in genetic recombination.
A reshuffling of genes occurs making individuals unique!!
Genetically DIFFERENT cell results
AND the forming tetrads of chromosomes

42. Formation of Haploid Cells (Sex cells)
During Anaphase I of Meiosis
Independent assortment the random separation of homologous chromosomes.
Results in genetic variation or mixing of genetic traits.
This is what allows you to have your dad’s color hair and your mother’s texture of hair!! 

43. Formation of Haploid Cells (Sex cells)
Meiosis II
Is very similar to Meiosis I, EXCEPT Meiosis II does NOT go through interphase again….
Instead, Meiosis II begins in prophase II and continues through “Pray More At The Church”
Meiosis II includes: prophase II, metaphase II, anaphase II, and telophase II.
Four new haploid cells result.

44. Meiotic Cell Division

45. Development of Gametes
Spermatogenesis is the process by which sperm cells are produced.
Oogenesis is the process that produces mature egg cells.

46. Meiosis in Male and Female Animals

47. Sexual Reproduction
Sexual reproduction is the formation of offspring through meiosis and the union of a sperm and an egg.
Offspring produced by sexual reproduction are genetically different from the parents.