Cell Cycle Mitosis & Meiosis Nancy Dow Jill Hansen Tammy Stundon December 1, 2012

1. Biology Partnership (A Teacher Quality Grant) Cell Cycle Mitosis & Meiosis Nancy Dow Jill Hansen Tammy Stundon December 1, 2012

2. Pre-test Q and A board What is Mitosis? What is Meiosis? When do they happen? What is alike and what is different about them?

3. Florida Next Generation Sunshine State Standards BENCHMARK SC.912.L.16.16 Describe the process of meiosis, including independent assortment and crossing over. Explain how reduction division results in the formation of haploid gametes or spores. (MODERATE) SC.912.L.16.17* Compare and contrast mitosis and meiosis and relate to the processes of sexual and asexual reproduction and their consequences for genetic variation. (HIGH) Clarifications Students will differentiate the processes of mitosis and meiosis. Students will describe the process of meiosis, including independent assortment and crossing over. Students will explain how meiosis results in the formation of haploid gametes or spores.

4. Content Limits • Items addressing mitosis or meiosis are limited to identification of phases, structures, and major events of each phase.

5. The cell cycle has four main stages. The cell cycle is a regular pattern of growth, DNA replication, and cell division.

6. Interphase prepares the cell to divide. During interphase, the DNA is duplicated. Mitosis and cytokinesis produce two genetically identical daughter cells. Parent cell centrioles spindle fibers centrosome nucleus with DNA

7. Mitosis divides the cell’s nucleus in four phases. • During prophase, chromosomes condense and nuclear membrane breaks down. • centrioles ‘move’ to the poles and spindle fibers form

8. Mitosis divides the cell’s nucleus in four phases. • During metaphase, chromosomes line up in the middle of the cell.

9. Mitosis divides the cell’s nucleus in four phases. • During anaphase, sister chromatids separate to opposite sides of the cell.

10. Mitosis divides the cell’s nucleus in four phases. • During telophase, the new nuclei form, spindle fibers break down and chromosomes begin to uncoil.

11. Cytokinesis differs in animal and plant cells. • In animal cells, the membrane pinches closed. • In plant cells, a cell plate forms. It's Mitosis---My-Sharona

13. For sexual reproduction

14. Number of chromosomes

15. KEY CONCEPT Gametes have half the number of chromosomes that body cells have.

16. Two types of cell divisions Mitosis – one cells divides to form TWO identical cells. Occurs for growth and repair Meiosis – a cell in the testes or ovaries divides into four cells which contain half the number of chromosomes. Occurs for reproduction (make gametes)

17. You have body cells and gametes. Body cells are also called somatic cells. Germ cells develop into gametes. Germ cells are located in the ovaries and testes. Gametes are sex cells: egg and sperm. Gametes have DNA that can be passed to offspring. sex cells (egg) body cells sex cells (sperm) Diploid (2n) Haploid (n)

18. INHERITANCE OF GENES Maternal chromosome pair Paternal chromosome pair Humans have 23 pairs of chromosomes (46 individual chromosomes) and, thus, two copies of each gene. Gene Maternal gamete: egg Paternal gamete: sperm Each human gamete has just one copy of each chromosome and, thus, one copy of each gene. Gametes unite during fertilization. Child inherits one set of chromosomes from each parent and, thus, two copies of each gene. ALLELES

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

20. Body cells are diploid; gametes are haploid. Fertilization between egg and sperm occurs in sexual reproduction. Diploid (2n) cells have two copies of every chromosome. Body cells are diploid. Half the chromosomes come from each parent.

21. Haploid (n) cells have one copy of every chromosome. • Gametes are haploid. • Gametes have 22 autosomes and 1 sex chromosome.

22. Chromosome number must be maintained in animals. • Many plants have more than two copies of each chromosome. • Mitosis and meiosis are types of nuclear division that make different types of cells. • Mitosis makesmore diploid cells

23. Meiosis makes haploid cells from diploid cells. • Meiosis occurs in sex cells. • Meiosis produces gametes.

24. Compare and Contrast

26. KEY CONCEPT During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

27. Meiosis Square Dance

28. Cells go through two rounds of division in meiosis. Meiosis reduces chromosome number and creates genetic diversity.

29. Meiosis I and meiosis II each have four phases, similar to those in mitosis. • Pairs of homologous chromosomes separate in meiosis I • Homologous chromosomes are similar but not identical. • Sister chromatids divide in meiosis II. • Sister chromatids are copies of the same chromosome. homologouschromosomes sister chromatids sister chromatids

30. HOMOLOGUES AND SISTER CHROMATIDS Homologues are the maternal and paternal copies of a chromosome. A sister chromatid is a chromosome and its identical duplicated version held together at a centromere. Homologues Homologues Replication (S Phase) Centromere Maternal chromosome Sister chromatids Paternal chromosome Sister chromatids

31. Meiosis I occurs after DNA has been replicated. • Meiosis I divides homologous chromosomes in four phases.

32. INTERPHASE Replicated chromosome Centromere Meiosis I Nuclear membrane INTERPHASE • Chromosomes replicate in preparation for meiosis.

33. MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE INTERPHASE Replicated chromosome Homologues Centromere Meiosis I Homologues cross over Nuclear membrane Spindle 1 INTERPHASE • Chromosomes replicate in preparation for meiosis. PROPHASE I • Replicated chromosomes condense. • Spindle apparatus is formed. • Homologous pairs of sister chromatids come together and cross over. • Nuclear membrane disintegrates.

34. Prophase I Biology Media Gallery Clip – Meiosis (2 min)

36. MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE Homologues Meiosis I Homologues cross over Spindle 2 1 PROPHASE I • Replicated chromosomes condense. • Spindle apparatus is formed. • Homologous pairs of sister chromatids come together and cross over. • Nuclear membrane disintegrates. METAPHASE I • Homologues move toward the center of the cell and line up.

37. MEIOSIS DIVISION 1: HOMOLOGUES SEPARATE Spindle fiber Meiosis I 2 METAPHASE I • Homologues move toward the center of the cell and line up. 3 ANAPHASE I • Homologues separate and are pulled to opposite poles. Sister chromatids going to each side are a mix of maternal and paternal genetic material.

38. Daughter cell 1 Spindle fiber Meiosis I Daughter cell 2 3 ANAPHASE I • Homologues separate and are pulled to opposite poles. Sister chromatids going to each side are a mix of maternal and paternal genetic material. 4 TELOPHASE I AND CYTOKINESIS • Sister chromatids arrive at the cell poles and the nuclear membrane reassembles around them. • The cell pinches into two daughter cells. • Chromosomes may unwind slightly.

39. Meiosis II divides sister chromatids in four phases. • DNA is not replicated between meiosis I and meiosis II.

40. MEIOSIS DIVISION 2: SISTER CHROMATIDS SEPARATE Daughter cell 1 Sister chromatids Daughter cell 2 4 TELOPHASE I AND CYTOKINESIS • Sister chromatids arrive at the cell poles and the nuclear membrane reassembles around them. • The cell pinches into two daughter cells. • Chromosomes may unwind slightly. 5 PROPHASE II • Chromosomes in daughter cells condense. 6 METAPHASE II • Sister chromatids line up at the center of the cell. 7 ANAPHASE II • Sister chromatid pairs are pulled apart by the spindle fibers toward opposite cell poles. There is a brief interphase prior to prophase II. Chromosomes are notreplicated again at this stage.

41. MEIOSIS DIVISION 2: SISTER CHROMATIDS SEPARATE Daughter cell 1 Daughter cell 2 Daughter cell 3 Daughter cell 4 7 ANAPHASE II • Sister chromatid pairs are pulled apart by the spindle fibers toward opposite cell poles. 8 TELOPHASE II AND CYTOKINESIS • The two daughter cells pinch into four haploid daughter cells. • The nuclear membrane reassembles around the chromosomes.

42. Why is meiosis so important? The chromosome number of the species remains the same generation after generation. The sperm and egg produced are NOT identical to the cells of the parents and this increases genetic diversity. Crossing over and independent assortment assure genetic diversity.

43. SOURCES OF GENETIC VARIATION There are multiple reasons why offspring are genetically different from their parents and one another. CROSSING OVER Crossing over during meiosis produces a mixture of maternal and paternal genetic material on each chromatid. REASSORTMENT OF HOMOLOGUES The homologues and sister chromatids distributed to each daughter cell during meiosis are a random mix of maternal and paternal genetic material. ALLELES COME FROM TWO PARENTS Each parent donates his or her own set of genetic material.

44. 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

45. Haploid cells develop into mature gametes. 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.

47. Mitosis vs. Meiosis Mitosis Occurs in every cell of the body (Somatic cells = body cells) One cell divides to form 2 identical cells Meiosis Occurs only in the testes and ovaries (sex cells) One cell divides TWICE to form 4 cells with half the number of chromosomes There are some small differences in the individual steps of both cycles… make note!

48. Chromosome number in humans 2n 46 chromosomes (23 pairs)  Diploid  mitosis produces diploid cells 1n  23 chromosomes  Haploid  meiosis forms haploid cells side by side comparison

49. Comparison of the cell cycles Group activity Side by side comparison of Mitosis and Meiosis

50. Foldable