LG: How do we produce gametes? Date: 2/4/13

1. LG: How do we produce gametes? Date: 2/4/13 Attention: from now on, if you see any words or phrases inside this “[ ]” symbol, you need to know them by heart!

2. [Mitosis] and [Meiosis] • Mitosis: -division of [somatic cells] = [body cells] • Meiosis -division of [gametes] = [sex cells]

3. Mitosis: Meiosis: Each resulting cell still has chromosomes from mom & dad

4. Mitosis Let’s Review!

5. [Asexual Reproduction] One parent Offspring [identical]=(clones) Quick No [variation]=difference

6. [Interphase] • Interesting things happen! • Cell preparing to [divide]=multiply • [Genetic material] doubles (making copies)

7. CENTROMERE GENES SISTER CHROMATID SISTER CHROMATID ONE CHROMOSOME ONE COPIED CHROMOSOME Sister Chromatid – each side of a replicated chromosome

8. [Prophase] • [Chromosomes] pair up! • Chromosomes thicken and shorten -become visible -2 chromatids joined by a [centromere] • [Centrioles] move to the opposite sides of the nucleus (only in animal cells) • [Nuclear membrane] disappears

9. [Metaphase] • Chromosomes meet in the middle! • Chromosomes arrange at equator of cell • Become attached to [spindle fibres] by centromeres • [Homologous chromosomes] do not pair up

10. What are homologous chromosomes? Definition: chromosomes having the same genes at the same loci (location) but possibly different alleles (alternative forms of a gene). For example, two chromosomes may have genes encoding eye color, but one may code for brown eyes, the other for blue.

11. [Anaphase] • Chromosomes get pulled apart • Spindle fibres contract pulling chromatids to the opposite poles of the cell

12. [Telophase/Cytokinesis] • Now there are two! • Nuclear envelope forms around chromosomes • Chromosomes uncoil • Cytokinesis • animals - pinching of plasma membrane • plants- elongates and the [cell plate] forms( future cell wall and cell membrane)

13. What is [meiosis] for? • Gametes for [Sexual Reproduction] • Two parents • Offspring all genetically different • Takes longer • Lots of variations

14. Meiosis • 4 [daughter cells] produced • Each daughter cell has half the chromosomes of the parent • 2 sets of [cell divisions] involved

15. Meiosis = reduction division • Meiosis • special cell division in sexually reproducing organisms • reduce number of chromosomes • 2n (46)  1n (23) • [diploid]  [haploid] • Reduced by half • makes [gametes] • [sperm], [eggs]

16. sex cells (egg) body cells sex cells (sperm) You have body cells and gametes. • Body cells are also called somatic cells. • Body cells cannot pass DNA on to offspring • Gametes are sex cells: egg and sperm. • Gametes have [DNA] that can be passed to offspring.

17. Your cells have [autosomes] and [sex chromosomes]. • Your body cells have 23 pairs of chromosomes. • Chromosome pairs 1-22 are autosomes. • Homologous pairs of chromosomes have the same structure. • For each homologous pair, one chromosome comes from each parent. • Sex chromosomes, X and Y, determine gender in mammals.

18. Once again! Homologous chromosomes

19. Body cells are diploid; gametes are haploid. • Diploid (2n) cells have two copies of every chromosome. • Body cells are diploid. • Half the chromosomes come from each parent.

20. Haploid (n) cells have one copy of every chromosome. • Gametes are haploid. • Gametes have 22 autosomes and 1 sex chromosome. • [Fertilization] restores the diploid number

21. Fertilization: sperm + egg in the fallopian tube (oviduct)

23. Meiosis Interphase The chromosomes have replicated, and they become visible. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

24. Meiosis Prophase I • The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one another • [Crossing over] occurs http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

25. Crossing over • 3 steps • cross over • breakage of DNA • re-fusing of DNA • New combinations of traits Tetrad

26. Crossing over contd. • Crossing Over of genes occurs now • The exchange of genetic material between homologous chromosomes • Results in new genetic combinations of offspring. • This is the main advantage of sexual reproduction Results in Variations!!

27. The homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles. Meiosis Metaphase I http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

28. The homologous chromosomes (not chromatids) move to opposite ends of the cell. Meiosis Anaphase I http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

29. The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of [maternal] and [paternal] chromosomes. Meiosis Telophase I & Cytokinesis http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

30. The cell has divided into two daughter cells. Meiosis Prophase II http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

31. Just like in Mitosis, the chromosomes line up in the middle on the spindle fibers. Meiosis Metaphase II http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

32. The two cells each begin to divide. As in Mitosis, the chromatids move to opposite ends of each cell. Meiosis Anaphase II http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

33. With the formation of four cells, meiosis is over. Each of these prospective gamete cells carries half the number of chromosomes of somatic cells. Telophase II &Cytokinesis http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html

34. [Gametogenesis] is the production of gametes. • Gametogenesis differs between females and males. • Sperm become streamlined and motile. • Sperm primarily contribute DNA to an embryo. • Eggs contribute DNA, cytoplasm, and organelles to an [embryo]. • During meiosis, the egg gets most of the contents; the other cells form [polar bodies].

35. Gametogenesis

36. Overview of Meiosis

38. Meiosis • Meiosis animation: http://www.youtube.com/watch?v=D1_-mQS_FZ0&NR=1

39. Similarities between Mitosis & Meiosis • Both are forms of nuclear division • Both involve [replication] • Both involve disappearance of the nuclear membrane • Both involve formation of spindle fibers

40. Comparison of Mitosis & Meiosis

41. Meiosis differs from mitosis in significant ways. • Meiosis has two cell divisions while mitosis has one. • In mitosis, homologous chromosomes never pair up. • Meiosis results in haploid cells; mitosis results in diploid cells.

42. Mitosis vs. Meiosis

43. Mitosis 1 division daughter cells genetically identical to parent cell produces 2 cells 2n  2n (diploid) produces cells for growth & repair no crossing over Meiosis 2 divisions daughter cells genetically different from parent produces 4 cells 2n  1n (haploid) produces gametes crossingover Mitosis vs. Meiosis

44. This may help you remember these terms: MITosis takes the cell and Makes It Two (diploid) Meiosis has to do with sex From the cell’s point of view: mITosis results in IdenTical Cells mEioSis results in Egg and Sperm (haploid) Clyde Freeman Herreid – Dept. of Biological Sciences: Buffalo State Univ. of New York

45. 46 46 46 46 46 46 46 46 46 46 23 23 46 23 23 Putting it all together… meiosis  fertilization  mitosis + development gametes meiosis egg zygote mitosis &development fertilization mitosis sperm

46. EMBRYO From one cell to many • A fertilized egg goes through an early stage of development called an embryo.

47. Inner: intestines Outer: skin cells Middle: bone cells Specialized cells perform specific functions. • Cells develop into their mature forms through the process of cell [differentiation]. • Cells differ because different combinations of genes are expressed.

48. The value of sexual reproduction • Sexual reproduction introduces genetic variation • genetic recombination during meiosis • independent assortment of chromosomes • random alignment of homologous chromosomes in Meiosis 1 • crossing over • mixing of alleles across homologous chromosomes • random fertilization • which sperm fertilizes which egg? • Driving evolution • variation for natural selection

49. Variation from random fertilization • Sperm + Egg = ? • any 2 parents will produce a zygote with over 70 trillion (223 x 223) possible diploid combinations

50. Michael & KirkDouglas Baldwin brothers Martin & Charlie Sheen, Emilio Estevez Sexual reproduction creates variability Sexual reproduction allows us to maintain both genetic similarity & differences.