Cell division

1. Cell division Mitosis & Meiosis

2. Cell Review • Cells have DNA, the information needed for life. • DNA is packaged into something called chromosomes.

3. Cell division All complex organisms originated from a single fertilized egg. Through cell division the numbers are increased Cell then specialise and change into their various roles (blood cell, bone cell, nerve cell, etc)

4. Why do cells divide? • Growth • Reproduction • Replacement of dying cells – skin, blood cells

5. Cell division in prokaryotes: Binary fission Bacteria have a single chromosome (versus the 46 humans have). • Chromosomes replicate • Cell membrane pushes inward • Cell divides in two, • each with a chromosome

7. Types of cell division in Eukaryotes • Mitosis: • Growth, development & repair • Asexual reproduction (yields identical cells) • Occurs in somatic (body) cells • Produces 2 identical cells • Meiosis: • Sexual reproduction (yields different cells) • Occurs in reproductive cells (gametes) • Produces 4 DIFFERENT cells

8. A comparison of mitosis and meiosis

9. Paper Plate Models • Each group will be in charge of making a paper plate model of mitosis. • Each person will find mitosis in the book and model each stage on a paper plate with yarn. • Yarn will represent the chromosomes. • Then the cell stages will be strung together to make a cell mobile.

10. Example • Write the name of the phase in back of the plate • Interphase • Prophase • Metaphase • Anaphase • Telophase

11. Mitosis • All daughter cells contain the same genetic information from the original parent cell from which it was copied. • Every different type cell in your body contains the same genes, but only some act to make the cells specialise into nerve or muscle tissue.

12. Mitosis overview Parent cell Chromosomes are copied and double in number Chromosomes now split 2 daughter cells identical to original

13. Mitosis

14. First step • Interphase begins first. • Chromosomes are copied • Chromosomes appear as thread (chromatin)

17. Prophase • Mitosis begins • Chromatin (DNA thread) condenses, causing the chromosomes to begin to become visible (X’s). • Centrioles appear and begin to move to opposite ends of cell. • Spindle fibers, made of microtubules, form between the poles • - Nucleolus disappears

20. 2. Metaphase - Chromosomes align on an axis called the metaphaseplate - Chromatids (or pairs of chromosomes) attach to the spindle fibers

22. 3. Anaphase - Chromatids (or pairs of chromosomes) separate at the centromere (center) and begin to move to opposite ends of the cell - Cell begins to elongate

24. 4. Telophase • Formation of nuclear membrane and nucleolus • Two new nuclei form • Chromosomes appear as chromatin (threads rather • than rods) • Mitosis ends. • Formation of the cleavagefurrow - a shallow groove in the cell near the old metaphase plate

26. Cytokinesis • Division of the cytoplasm • AT THE END the daughter cells have the SAME number of chromosomes as the PARENT/MOTHER cell.

28. Mitosis Flip Book • You will complete each page to illustrate the changes that take place in a cell during cell division. • The first oval (or ovals) in EACH phase should show the location of the organelles at that stage. • Use the extra ovals to show the movement of organelles between stages. • Write a brief description of each stage on the blank side of your page. Interphase Interphase is the stage where….

29. Mitosis Animated animation

30. Mitosis

33. Mitosis in an onion root Can you identify some of the stages of Mitosis here?

34. Anaphase Interphase Telophase Metaphase Prophase

35. Meiosis • Type of cell division that halves number of chromosomes • 1N is one chromosome • 2N is two chromosome (sister chromatids) • 2 divisions involved • Product is gamete, essential for sexual reproduction 2N 1N

36. Terms • Homologous Chromosome: a chromosome that has the same DNA (ex: 2 of the same chromosomes that hold the DNA for hair color and eye color.) • Crossing over: when the chromosome from the male and from the female swap DNA.

37. Overview of meiosis: how meiosis reduces chromosome number In Metaphase I, Homologous chromosomes line up next to each other In Prophase I, Homologous chromosomes cross over and swap DNA. This allows diversity in offspring. First part of meiosis involves separating homologous chromosomes Second part involves separating chromatids Homologous Same chromosome

38. Overview of meiosis: how meiosis reduces chromosome number In Anaphase I, Homologous chromosomes Are pulled apart. In Telophase I, Homologous chromosomes are in separate cells. First part of meiosis involves separating homologous chromosomes Second part involves separating chromatids homologous

39. Overview of meiosis: how meiosis reduces chromosome number In Prophase II, there is no REPLICATION or Crossing over. In Anaphase II, chromatid (2N) separates, moving one chromosome (1N) per cell. First part of meiosis involves separating homologous chromosomes In metaphase II, Chromosomes line up in the 2 cells. In Telophase II, each of the 4 daughter cells should have one copy of each chromosome. Cells are NOT identical due to crossing over and swapping DNA. Second part involves separating chromatids

40. The results of crossing over during meiosis • Crossing over helps to promote genetic variation. • Two homologous chromosomes can code for the same traits, but the variety in the traits may be different. • Example: single gene controls the color of flower petals, but there may be several different versions of the gene.

41. Evolutionary advantage • asexual reproduction (mitosis) • easy, rapid, effective way to reproduce • useful in stable environment • lack of genetic diversity among offspring • sexual reproduction (meiosis) • promotes genetic variability • useful in changing environment