1. Cellular Reproduction (Cell Division) Mitosis and Meiosis

2. Cell Division Cells must divide after they reach a certain size. Otherwise, their surface area becomes too small for their volume (Surface:Volume ratio) Before they divide, they must make copies of all the information they contain It’s sort of like backing up your hard drive so you can copy the files to a new computer. only using chromosomes instead of hard drives. That’s what the process of MITOSIS is all about... Copying information.

3. The Cell Cycle (the life cycle of the cell) The cell spends more than ¾ of its life cycle growing and preparing to divide (INTERPHASE) While it is growing, it also begins to replicate its DNA When it is ready to divide, MITOSIS, the process of dividing its DNA, begins. When the DNA has been evenly split, Cytokinesis (division) occurs.

4. DNA and Chromosomes In humans, the information needed to build all the proteins and enzymes you need for your cells to function is stored in a chemical called DNA (Deoxyribose Nucleic Acid) This DNA is found in the nucleus of every cell of your body (except red blood cells) Every cell has (in theory) the information needed to make an entire body.

6. Anatomy of a Chromosome Chromosomes hold the DNA in the nucleus, all coiled up. Chromosome Supercoils Coils of DNA Nucleosome Histones (proteins that give DNA more strength) DNA (double helix)

7. YouTube Videos Zoom in on DNA Wrapped up DNA Nucleosomes & chromatin

8. Terminology preview Chromosome: a structure composed of DNA and some proteins that contains the genetic information. Just before division a chromosome may contain two sister chromatids. Chromatid: a half a chromosome– before a cell divides its chromosomes appear to be “double width” and is made of two chromatids. Gene: The portion of a chromosome that contains enough DNA to code for one specific trait. Diploid: A cell that contains a full “double set” of chromosomes (half from the mother, half from the father). Normal body cells are diploid. Haploid: a cell that contains only one set of chromosomes (half the normal number). Egg and sperm cells are haploid Homologous : In a diploid cell the chromosomes are “paired”. Each pair is said to be homologous, meaning they resemble each other.

9. Enrichment: A bunches of “chromes” and “somes” In addition to the words defined before, you will find lots more words that either start with “chrom” or end with “some” Chromatid, Chromosome, Chromatin, Chromatography Chromosome, Centrosome, Lysosome, Ribosome. “Chromo” means “coloured”. Since DNA picks up dyes easily, anything made of DNA can be easily identified under the microscope. Many things made of, or containing, DNA start with chrom- or chromo-. “Soma” or “some” means “body”. In biology this is usually a tiny body, so organelles or cell structures often end in -some.

10. Cell Division in Eukaryotes Eukaryotes (organisms with complete cells) have two types of cell division: –Mitosis (normal cell division) –Meiosis (cell division for reproduction) The examples are all from eukaryotes. Prokaryotes (simple cells like bacteria) undergo a similar, but slightly simpler, process called “binary fission” –This will not be studied in any detail this year, just think of binary fission as “mitosis-light”

11. Mitosis and normal cells Normal body cells are Diploid, which means that they have a double set of chromosomes In humans, this is 2x23=46 chromosomes 46 is the “human diploid number” In Mitosis, all chromosomes are duplicated before the cell divides. In humans, this means that each cell starts with 46 chromosomes before it divides, and the new cells each end up with 46 chromosomes after division.

12. Steps in the Cell Cycle Remember: IPMAT It will help you keep track of the 5 main phases of a cell’s life = INTERPHASE = PROPHASE = METAPHASE = ANAPHASE = TELOPHASE Preparing for Mitosis Undergoing Mitosis Where’s my Pee MAT?

13. Animated Diagram of Mitosis The next slide shows an animated version of the main steps of mitosis. Just watch and follow what happens. More detailed descriptions will follow.

14. Mitosis Interphase: The Cell grows and the DNA replicates. The cell prepares to divide. Prophase: The nuclear envelope disapears and the centrioles migrate to opposite poles of the cell Metaphase: The chromosomes line up near the middle of the cell (equatorial plane) and spindle fibres attach to them. Anaphase: The chomatids split into new chromosomes, and the new chromosome migrate to opposite poles Telophase: The chromosomes reach the poles, new nuclei begin to form, the cell prepares to split. Cytokinesis: The cell splits into two new cells Centrosome (centrioles) Nucleus Chromosomes

15. MITOSIS in Detail The following slides show more detail of how mitosis occurs. The photographs are of a plant cell. Animal cells are similar, but the centrosomes are visible in animals, but not in plant cells.

16. INTERPHASE Interphase is the time during which a cell matures, grows, and duplicates its DNA The cell spends most of its life in interphase Your book identifies 3 parts of interphase: –G1: The cell grows and matures –S: The DNA replicates –G2: The cell grows some more, in preparation for mitosis.

17. Photograph of Interphase

18. PROPHASE DNA coils up to form chromosomes each chromosome has 2 chromatids Two centrosomes appear. These are fibre anchoring points near the nucleus. In animal cells there are tiny organelles (centrioles) inside the centrosomes. Plant cells don’t have visible centrioles. The centrosomes move towards opposite ends In this plant cell you won’t see them. The nuclear membrane disappears (breaks up) The centrosomes produce “spindle fibres” made of 2 varieties of microtubules. Kinetochore fibres: attach to the chromosomes Polar fibres: extend from one centrosome to the other.

19. Photo: Early Prophase Chromosomes

20. METAPHASE During metaphase the kinetochore (spindle) fibers move the chromosomes to the center of the dividing cell. The chromosomes line up along the equatorial plane (middle) of the cell. Kinetochore fibers are attached to each chromatid, near the centromere.

21. Photo: Metaphase Centrosome location (this is a plant cell, so the centrioles are not visible) Chromosomes Equatorial Plane Spindle (fibers)

22. ANAPHASE The chromatids separate They move towards opposite ends of the cell From this point on, each chromatid is considered to be a new chromosome.

23. Photo: Anaphase Equatorial Plane Chromosomes Centrosome location

24. TELOPHASE Chromosomes reach the opposite ends of the cell. Chromosomes begin to uncoil, changing back into chromatin. Nuclear membranes begin to form on each side of the cell CYTOKINESIS begins.

25. CYTOKINESIS As TELOPHASE ends, the cell divides into two new cells. A cleavage furrow forms, and pinches the cell apart. There are now two cells, each with a full set of chromosomes (ie. Diploid)

26. Photo: Telophase & Cytokinesis Cleavage furrow Nucleus forming Cells Divide

27. Videos Serious MITOSIS DescriptionMITOSIS Description Mitosis introduction Mind BitesMind Bites The most annoying MITOSIS song ever!MITOSIS song MITOSIS animationMITOSIS animation. Silent MITOSIS Silent MITOSIS animation

28. MEIOSIS Meiosis is good for sex! M MM 1/21/2 Meiosis is a process of cell division that reduces the number of chromosomes in a cell by half. Meiosis occurs in the reproductive organs. In humans, meiosis produces ova (egg) or sperm cells. This is necessary for sexual reproduction. Visually, meiosis resembles mitosis (phases: P.M.A.T.) but twice! Prophase I, Metaphase I, Anaphase I, Telophase I Prophase II, Metaphase II, Anaphase II, Telophase II

29. Why is Meiosis so Important? It’s only important to organisms that reproduce sexually! If meiosis didn’t occur, then the egg and sperm cells would have the same number of chromosomes as the body cells When fertilization occurred, there would be too many chromosomes!

30. Meiosis, First Division. Homologous Chromosomes Line up Remember: Humans have 46 chromosomes in each cell. These are actually 23 pairs of homologous chromosomes (23 maternal, 23 paternal) During the first metaphase of MEIOSIS, the chromosomes line up in homolgous pairs. When anaphase starts, the chromatids don’t break apart (unlike mitosis), instead whole chromosomes (including both chromatids) move to each side of the cell.

31. Meiosis, Fist Division (continued) Crossing Over Normally the genes on one chromosome travel together... but sometimes during meiosis, a gene from one chromosome may switch places (or cross over) with the corresponding gene on the homologous chromosome that lines up beside it during the first division of meiosis. Crossing over helps randomize the distribution of genes from parent to offspring

32. Meiosis, Second division Chromatids finally split. After the first division of meiosis, both human cells have 23 chromosomes (instead of the normal 46), but each chromosome still has two chromatids. A second division occurs, this time the chromatids do split (more like mitosis), giving four cells with 23 chromosomes each. For Diagrams of Meiosis, See pages 154 and 155

33. After Meiosis: Production of Gametes Spermatogenesis Oogenesis In the male, each cell that undergoes meiosis produces four spermatids, that later grow tails (flagella) and become sperm cells. In the female, each cell that undergoes meiosis produces one large ovum and three tiny polar bodies. The ovum survives to become an egg, and the three polar die and disintegrate.

34.  Single division  Double division Diploid Body Cells Haploid Gamete Cells Mitosis Meiosis

35. More about Human Chromosomes This picture shows the chromosome map (or karyotype) of a normal human, showing the chromosomes as they would appear immediately after mitosis. It consists of 22 numbered pairs of neatly matched homologous chromosomes (called the autosomes) The last pair (called the sex chromosomes) is not numbered, and are only neatly matched in females (XX). In males, they are mismatched (XY)

36. Assignments Read chapter summaries –Page 157 Do End of Chapter Questions –Page 158 # 1 to 20

37. End of Chapter Questions 1.A chromosome is made of DNA and histone proteins, tightly wound into rod-shaped structures. Homologous chromosomes are pairs of morphologically similar chromosomes. 2.Mitosis is normal division of the cell nucleus. Meiosis is division of the cell nucleus to form gametes (sex cells). Cytokinesis is the division of the cell cytoplasm into two new cells. 3.Autosomes are the normal, paired homologous chromosomes. Sex chromosomes are a dissimilar pair of chromosomes used in sex determination (XX or XY)

38. 4. Kinetochore fibres attach to the center (or centromere) of the chromosomes during metaphase (of mitosis). Polar fibres connect one centrosome to the other. Both are types of spindle fibres. 5. A Diploid cell has a complete (double) set of matching homologous pairs of chromosomes (2 of each type). A Haploid cell has only one of each of the homologous chromosomes. (1 of each type).

39. 6.D) Prokaryotic chromosomes consist of a circular DNA molecule. 7.C) A chromatid one of two identical parts that make up a (mature) chromosome. 8.B) Every species has a distinctive number of chromosomes per cell. 9.D) Binary fission is prokaryotic cell division 10.A) Mitosis can increase the number of body cells without changing the information contained in the cells’ DNA 11.D) Interphase is a time of cell growth and development (not A, since there is no G3 phase)

40. 12. A) Cytokinesis differs in plant and animal cells. 13. A) Spermatogenesis produces four haploid cells (called sperm) 14. B) Oogenesis requires meiotic cell divisions. 15. D) Crossing over occurs during meiosis I