1. LECTURE PRESENTATIONS For CAMPBELL BIOLOGY, NINTH EDITION Jane B. Reece, Lisa A. Urry, Michael L. Cain, Steven A. Wasserman, Peter V. Minorsky, Robert B. Jackson © 2011 Pearson Education, Inc. Lectures by Erin Barley Kathleen Fitzpatrick Meiosis and Sexual Life Cycles Chapter 13

2. Overview: Variations on a Theme Living organisms are distinguished by their ability to _______________their own kind ____________is the scientific study of heredity and variation _____________is the transmission of traits from one generation to the next _____________is demonstrated by the differences in appearance that offspring show from parents and siblings © 2011 Pearson Education, Inc.

3. Concept 13.1: Offspring acquire genes from parents by inheriting chromosomes In a literal sense, children do not inherit particular physical traits from their parents It is _________that are actually inherited © 2011 Pearson Education, Inc.

4. Inheritance of Genes ______________ are the units of heredity, and are made up of segments of DNA Genes are passed to the next generation via reproductive cells called __________ (sperm and eggs) Each gene has a specific location called a ____________ on a certain chromosome Most DNA is packaged into ______________ © 2011 Pearson Education, Inc.

5. Comparison of Asexual and Sexual Reproduction In ________________________, a single individual passes genes to its offspring without the fusion of gametes A _____________ is a group of genetically identical individuals from the same parent In ______________________, two parents give rise to offspring that have unique combinations of genes inherited from the two parents © 2011 Pearson Education, Inc.

6. Figure 13.2 (a) Hydra (b) Redwoods Bud Parent 0.5 mm

7. Concept 13.2: Fertilization and meiosis alternate in sexual life cycles A _____________ is the generation-to- generation sequence of stages in the reproductive history of an organism © 2011 Pearson Education, Inc.

8. Sets of Chromosomes in Human Cells Human ________________ (any cell other than a gamete) have 23 pairs of chromosomes A _______________ is an ordered display of the pairs of chromosomes from a cell The two chromosomes in each pair are called ___________________________, or homologs Chromosomes in a ____________________ are the same length and shape and carry genes controlling the same inherited characters © 2011 Pearson Education, Inc.

9. Figure 13.3b Pair of homologous duplicated chromosomes Centromere Sister chromatids Metaphase chromosome 5  m

10. The _____________________, which determine the sex of the individual, are called X and Y Human ________________ have a homologous pair of X chromosomes (XX) Human ____________ have one X and one Y chromosome The remaining 22 pairs of chromosomes are called _________________ © 2011 Pearson Education, Inc.

11. Each pair of homologous chromosomes includes ______________________ from each parent The 46 chromosomes in a human somatic cell are _____________________: one from the mother and one from the father A ____________________ (2n) has two sets of chromosomes For humans, the diploid number is ___________ © 2011 Pearson Education, Inc.

12. In a cell in which DNA synthesis has occurred, each chromosome is __________________ Each replicated chromosome consists of two identical __________________________ © 2011 Pearson Education, Inc.

13. Figure 13.4 Sister chromatids of one duplicated chromosome Key Maternal set of chromosomes (n  3) Paternal set of chromosomes (n  3) Key 2n  6 Centromere Two nonsister chromatids in a homologous pair Pair of homologous chromosomes (one from each set)

14. A gamete (sperm or egg) contains a single set of chromosomes, and is _______________ (n) For humans, the haploid number is __________ Each set of 23 consists of 22___________ and a single _________________________ In an unfertilized _______________, the sex chromosome is X In a ____________ cell, the sex chromosome may be either X or Y © 2011 Pearson Education, Inc.

15. ___________________ is the union of gametes (the sperm and the egg) The fertilized egg is called a ____________ and has one set of chromosomes from each parent The zygote produces somatic cells by ________ and develops into an adult Behavior of Chromosome Sets in the Human Life Cycle © 2011 Pearson Education, Inc.

16. At sexual maturity, the ovaries and testes produce ________________________ Gametes are the only types of human cells produced by ___________, rather than mitosis Meiosis results in ______________ of chromosomes in each gamete __________________ and ______________ alternate in sexual life cycles to maintain chromosome number © 2011 Pearson Education, Inc.

17. Figure 13.5 Key Haploid (n) Diploid (2n) Egg (n) Haploid gametes (n  23) Sperm (n) Ovary Testis Mitosis and development Diploid zygote (2n  46) Multicellular diploid adults (2n  46) MEIOSIS FERTILIZATION

18. The Variety of Sexual Life Cycles The alternation of meiosis and fertilization is common to all organisms that reproduce _______________ The three main types of sexual life cycles differ in the ____________ of meiosis and fertilization © 2011 Pearson Education, Inc.

19. _____________ are the only haploid cells in animals They are produces by ___________ and undergo no further cell division before fertilization Gametes fuse to form a ________________ that divides by mitosis to develop into a multicellular organism © 2011 Pearson Education, Inc.

20. Figure 13.6a Key Haploid (n) Diploid (2n) Gametes MEIOSIS FERTILIZATION Zygote Mitosis Diploid multicellular organism (a) Animals n 2n2n n n 2n2n

21. Plants and some algae exhibit an ___________ ___________________________ This life cycle includes both a diploid and haploid ____________________________ The diploid organism, called the ____________, makes haploid spores by _________________ © 2011 Pearson Education, Inc.

22. Each spore grows by ____________ into a haploid organism called a _________________ A gametophyte makes haploid ______________ ___________________ Fertilization of gametes results in a __________ _____________________ © 2011 Pearson Education, Inc.

23. Figure 13.6b 2n2n 2n2n n MEIOSISFERTILIZATION Mitosis Gametes Spores Zygote Haploid multi- cellular organism (gametophyte) Diploid multicellular organism (sporophyte) (b) Plants and some algae n n n n Haploid (n) Diploid (2n) Key

24. In most _______________________, the only diploid stage is the single-celled zygote; there is no multicellular diploid stage The zygote produces haploid cells by ____________ Each haploid cell grows by mitosis into a ____________________________________ The haploid adult produces gametes by _______________ © 2011 Pearson Education, Inc.

25. Figure 13.6c Key Haploid (n) Diploid (2n) 2n2n n n n n n MEIOSIS FERTILIZATION Mitosis Gametes Zygote Haploid unicellular or multicellular organism (c) Most fungi and some protists

26. Depending on the type of life cycle, either haploid or diploid cells can divide by ________ However, only ______________ cells can undergo meiosis In all three life cycles, the halving and doubling of chromosomes contributes to __________________________ in offspring © 2011 Pearson Education, Inc.

27. Concept 13.3: Meiosis reduces the number of chromosome sets from diploid to haploid Like mitosis, meiosis is preceded by the _________________________________ Meiosis takes place in two sets of cell divisions, called __________ and __________ The two cell divisions result in ___________ _________________, rather than the two daughter cells in mitosis Each daughter cell has only _________as many chromosomes as the parent cell © 2011 Pearson Education, Inc.

28. The Stages of Meiosis After chromosomes duplicate, two divisions follow –____________ (reductional division): homologs pair up and separate, resulting in two haploid daughter cells with replicated chromosomes –____________ (equational division) sister chromatids separate The result is four haploid daughter cells with ___________________ chromosomes © 2011 Pearson Education, Inc.

29. Figure 13.7-1 Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes Chromosomes duplicate Sister chromatids Diploid cell with duplicated chromosomes Interphase

30. Figure 13.7-3 Pair of homologous chromosomes in diploid parent cell Duplicated pair of homologous chromosomes Chromosomes duplicate Sister chromatids Diploid cell with duplicated chromosomes Homologous chromosomes separate Haploid cells with duplicated chromosomes Sister chromatids separate Haploid cells with unduplicated chromosomes Interphase Meiosis I Meiosis II 21

31. Meiosis I is preceded by ___________, when the chromosomes are duplicated to form sister chromatids The sister chromatids are genetically ___________ and joined at the centromere The single ________________ replicates, forming two centrosomes © 2011 Pearson Education, Inc.

32. Division in meiosis I occurs in four phases – _____________ – ________________________________ © 2011 Pearson Education, Inc.

33. Figure 13.8 MEIOSIS I: Separates homologous chromosomes Prophase I Metaphase IAnaphase I Telophase I and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Duplicated homologous chromosomes (red and blue) pair and exchange segments; 2n  6 in this example. Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Chromosomes line up by homologous pairs. Sister chromatids remain attached Homologous chromosomes separate Each pair of homologous chromosomes separates. Cleavage furrow Two haploid cells form; each chromosome still consists of two sister chromatids. MEIOSIS I: Separates sister chromatids Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing unduplicated chromosomes.

34. Figure 13.8a Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis Centrosome (with centriole pair) Sister chromatids Chiasmata Spindle Homologous chromosomes Fragments of nuclear envelope Duplicated homologous chromosomes (red and blue) pair and exchange segments; 2n  6 in this example. Centromere (with kinetochore) Metaphase plate Microtubule attached to kinetochore Chromosomes line up by homologous pairs. Sister chromatids remain attached Homologous chromosomes separate Each pair of homologous chromosomes separates. Cleavage furrow Two haploid cells form; each chromosome still consists of two sister chromatids.

35. _______________ Prophase I typically occupies more than ____ of the time required for meiosis ___________ begin to condense In ____________, homologous chromosomes loosely pair up, aligned gene by gene © 2011 Pearson Education, Inc.

36. In ________________, nonsister chromatids exchange DNA segments Each pair of chromosomes forms a _________, a group of ____________________ Each tetrad usually has one or more _________________, X-shaped regions where crossing over occurred © 2011 Pearson Education, Inc.

37. ________________ In metaphase I, ___________________ at the metaphase plate, with one chromosome facing each pole Microtubules from one pole are attached to the kinetochore of ______________________ of each tetrad Microtubules from the other pole are attached to the kinetochore of the _____________________ © 2011 Pearson Education, Inc.

38. _______________ In anaphase I, _______________ of homologous chromosomes ________________ ______________________ moves toward each pole, guided by the spindle apparatus Sister chromatids ______________________ at the centromere and move as one unit toward the pole © 2011 Pearson Education, Inc.

39. _______________________ In the beginning of telophase I, each half of the cell has a ____________ set of chromosomes; each chromosome still consists of two sister chromatids ___________________ usually occurs simultaneously, forming two haploid daughter cells © 2011 Pearson Education, Inc.

40. In animal cells, a ___________________ forms; in plant cells, a cell plate forms No chromosome _________________ occurs between the end of meiosis I and the beginning of meiosis II because the chromosomes are already replicated © 2011 Pearson Education, Inc.

41. Division in meiosis II also occurs in four phases –_________________ –________________________________ Meiosis II is very similar to __________________ © 2011 Pearson Education, Inc.

42. Figure 13.8b Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Sister chromatids separate Haploid daughter cells forming During another round of cell division, the sister chromatids finally separate; four haploid daughter cells result, containing unduplicated chromosomes.

43. __________________ In prophase II, a spindle apparatus forms In late prophase II, chromosomes (each ___ ____________________________) move toward the metaphase plate © 2011 Pearson Education, Inc.

44. ___________________ In metaphase II, the __________________ are arranged at the metaphase plate Because of ____________________ in meiosis I, the two sister chromatids of each chromosome are no longer genetically identical The kinetochores of _____________________ attach to microtubules extending from opposite poles © 2011 Pearson Education, Inc.

45. ___________________ In anaphase II, the ____________________ separate The sister chromatids of each chromosome now move as two newly ______________ __________________ toward opposite poles © 2011 Pearson Education, Inc.

46. ______________________ In telophase II, the chromosomes arrive at ____________________________ _______________ form, and the chromosomes begin decondensing © 2011 Pearson Education, Inc.

47. __________________ separates the cytoplasm At the end of meiosis, there are four daughter cells, each with a _______________________ ____________________ Each daughter cell is ___________ _______ from the others and from the parent cell © 2011 Pearson Education, Inc.

48. A Comparison of Mitosis and Meiosis Mitosis ________________ the number of chromosome sets, producing cells that are genetically identical to the parent cell Meiosis ______________ the number of chromosomes sets from two (diploid) to one (haploid), producing cells that differ genetically from each other and from the parent cell © 2011 Pearson Education, Inc.

49. Figure 13.9 Prophase Duplicated chromosome MITOSIS Chromosome duplication Parent cell 2n  6 Metaphase Anaphase Telophase 2n2n 2n2n Daughter cells of mitosis MEIOSIS MEIOSIS I MEIOSIS II Prophase I Metaphase I Anaphase I Telophase I Haploid n  3 Chiasma Chromosome duplication Homologous chromosome pair Daughter cells of meiosis I Daughter cells of meiosis II n n n n SUMMARY Property Mitosis Meiosis DNA replication Number of divisions Synapsis of homologous chromosomes Number of daughter cells and genetic composition Role in the animal body Occurs during interphase before mitosis begins One, including prophase, metaphase, anaphase, and telophase Does not occur Two, each diploid (2n) and genetically identical to the parent cell Enables multicellular adult to arise from zygote; produces cells for growth, repair, and, in some species, asexual reproduction Occurs during interphase before meiosis I begins Two, each including prophase, metaphase, anaphase, and telophase Occurs during prophase I along with crossing over between nonsister chromatids; resulting chiasmata hold pairs together due to sister chromatid cohesion Four, each haploid (n), containing half as many chromosomes as the parent cell; genetically different from the parent cell and from each other Produces gametes; reduces number of chromosomes by half and introduces genetic variability among the gametes

50. Three events are unique to meiosis, and all three occur in meiosis l –__________________________ in prophase I: Homologous chromosomes physically connect and exchange genetic information –At the metaphase plate, there are _________ _____________________________, instead of individual replicated chromosomes –At anaphase I, it is _________________ _____________________, instead of sister chromatids, that separate © 2011 Pearson Education, Inc.

51. Sister chromatid _____________ allows sister chromatids of a single chromosome to stay together through meiosis I Protein complexes called ______________ are responsible for this cohesion In mitosis, cohesins are _____________ at the end of metaphase In meiosis, cohesins are cleaved along the chromosome arms in __________________ (separation of homologs) and at the centromeres in anaphase II (separation of sister chromatids) © 2011 Pearson Education, Inc.

52. Concept 13.4: Genetic variation produced in sexual life cycles contributes to evolution ________________ (changes in an organism’s DNA) are the original source of genetic diversity Mutations create different versions of genes called _____________ _________________________ during sexual reproduction produces genetic variation © 2011 Pearson Education, Inc.

53. Origins of Genetic Variation Among Offspring The behavior of chromosomes during _________________________________ is responsible for most of the variation that arises in each generation Three mechanisms contribute to genetic variation –________________________________ © 2011 Pearson Education, Inc.

54. Independent Assortment of Chromosomes Homologous pairs of chromosomes orient _________________________ of meiosis In ___________________________, each pair of chromosomes sorts maternal and paternal homologs into daughter cells independently of the other pairs © 2011 Pearson Education, Inc.

55. The number of combinations possible when chromosomes assort independently into gametes is ____, where n is the ____________ _______________ For humans (n = ____), there are more than ___ __________ (2 23 ) possible combinations of chromosomes © 2011 Pearson Education, Inc.

56. Figure 13.10-3 Possibility 1 Possibility 2 Two equally probable arrangements of chromosomes at metaphase I Metaphase II Daughter cells Combination 1 Combination 2Combination 3Combination 4

57. Crossing Over Crossing over produces __________________, which combine DNA inherited from each parent Crossing over begins very early in _____________, as homologous chromosomes pair up gene by gene © 2011 Pearson Education, Inc.

58. In crossing over, homologous portions of two _________________________ trade places Crossing over contributes to _____________ ___________________ by combining DNA from two parents into a single chromosome © 2011 Pearson Education, Inc.

59. Figure 13.11-5 Prophase I of meiosis Nonsister chromatids held together during synapsis Pair of homologs Chiasma Centromere TEM Anaphase I Anaphase II Daughter cells Recombinant chromosomes

60. Random Fertilization _____________________ adds to genetic variation because any sperm can fuse with any ovum (unfertilized egg) The fusion of two gametes (each with 8.4 million possible chromosome combinations from independent assortment) produces a zygote with any of about _______________ diploid combinations © 2011 Pearson Education, Inc.

61. ___________________ adds even more variation Each zygote has a _________________________ © 2011 Pearson Education, Inc.

62. Animation: Genetic Variation Right-click slide / select “Play”

63. The Evolutionary Significance of Genetic Variation Within Populations ______________ ____________ results in the accumulation of genetic variations favored by the environment ________________ _____________ contributes to the genetic variation in a population, which originates from __________________ © 2011 Pearson Education, Inc.