Cell division- meiosis

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Cell division- meiosis

  1. 1. (4 Periods)
  2. 2. State StandardsGenetics State Standards 10.4 In sexually reproducing organism, each offspring contains a mix of characteristics inherited from both parents.Genetics CAPT Strands D 34. Describe, in general terms, how the genetic information of organisms can be altered to make them produce new materials. D 35. Explain the risks and benefits of altering the genetic composition and cell products of existing organisms. D 36. Explain how meiosis contributes to the genetic variability of organisms.
  3. 3. Objectives Understand that most organisms have two genes for each trait. Illustrate how meiosis contributes to genetic variability. Create a visual representation of the stages of meiosis.
  4. 4. Meiosis The process to make cells with half the number of chromosomes for sexual reproduction Occurs in our germ cells that produce gametes  Sperm & egg Results in four cells genetically different from parent cell and from each other Haploid (n) cells
  5. 5. Why Do We Need Meiosis? It is the fundamental basis of sexual reproduction Two haploid (n) gametes are brought together through fertilization to form a diploid (2n) zygote If egg and sperm had the same number of chromosomes as other body cells then the offspring would have too many chromosomes.
  6. 6. Meiosis Meiosis must reduce the chromosome number by half (n) Fertilization then restores the 2n number from mom from dad child too much! meiosis reduces genetic content The right number!
  7. 7. Fertilization 2n = 6 n =3
  8. 8. Meiosis-Replication Replication is the process of duplicating a chromosome Occurs prior to division Replicated copies are called sister chromatids Held together at centromere
  9. 9. Meiosis Gene Z Homologous Sister chromosomes Chromatids (same genes, (same genes,different alleles) same alleles)  Homologous chromosomes are the same size & shape  Carry genes for the same trait but are not identical!
  10. 10. CheckpointMeiosis results in ____. 1. 4 identical cells 2. 4 genetically different cells 3. 2 genetically different cells 4. 2 identical cells
  11. 11. CheckpointHomologous chromosomes are _____. 1. Same in size 2. Same in shape 3. Carry genes for the same trait 4. All of the above
  12. 12. CheckpointWhy do we need meiosis?A: To reduce the chromosome number in gametes, otherwise offspring would have too many chromosomes
  13. 13. Meiosis Sister chromatids separate Homologous chromosomes separate Meiosis I Meiosis IIDiploid Diploid Haploid
  14. 14. Meiosis I SpindleNucleus fibers Nuclear envelopeEarly Prophase I Telophase I(Chromosome Late Prophase I Metaphase I Anaphase I (haploid)# doubled)
  15. 15. Prophase IEarly prophase Late prophase Homologous pair.  Chromosomes condense. Crossing over occurs.  Spindle forms.  Nuclear envelope fragments.
  16. 16. Prophase I : Crossing-Over Synapsis – the pairing of homologous chromosomes  Group of 4 chromatids Homologous chromosomes Join to form a (each with sister chromatids) TETRAD
  17. 17. Prophase I : Crossing-Over Homologous chromosomes in a tetrad cross over each other Pieces of chromosomes or genes are exchanged Produces genetic recombination in the offspring
  18. 18. Prophase I : Crossing-Over Homologous chromosomes during crossing-over
  19. 19. Metaphase I  Homologous pairs of chromosomes align along the equator of the cell
  20. 20. Anaphase I Homologous chromosomes separate and move to opposite poles. Sister chromatids remain attached at their centromeres.
  21. 21. Telophase I Nuclear envelopes reassemble. Spindle disappears. Cytokinesis divides cell into two.
  22. 22. Meiosis II Only one of the homologous pairGene Z of chromosome is present in the cell. Sister chromatids carry identical genetic information.Meiosis II produces gametes with one copy of eachchromosome and thus one copy of each gene.
  23. 23. Meiosis IIProphase II Metaphase II Anaphase II Telophase II 4 different haploid cells
  24. 24. Prophase II Nuclear envelope fragments.  Spindle forms.
  25. 25. Metaphase II Chromosomes align along equator of cell.
  26. 26. Anaphase II Pole Sister chromatids separate and move to opposite poles. Equator 26
  27. 27. Telophase II Nuclear envelope assembles. Chromosomes unwind. Spindle disappears. Cytokinesis divides cell into two.
  28. 28. Results of Meiosis  Gametes (egg & sperm) form  Four haploid cells (n) with one copy of each chromosome  One allele of each gene  Different combinations of alleles for different genes along the chromosome
  29. 29. CheckpointWhich best describes crossing-over? 1. Pieces of genes are exchanged 2. Allow genetic variation 3. Occurs in Prophase I 4. All of the above
  30. 30. CheckpointDuring anaphase I in meiosis what is pulled apart? 1. Centromere 2. Homologous chromosomes 3. Sister chromatids 4. Spindle fibers
  31. 31. CheckpointWhich best describes a haploid cell? 1. n 2. Half the genetic information 3. Gametes 4. All of the above
  32. 32. Spermatogenesis Occurs in the testes Two divisions produce 4 spermatids Spermatids mature into sperm Men produce about 250,000,000 sperm per day
  33. 33. Spermatogenesis Spermatid
  34. 34. Oogenesis Occurs in the ovaries Two divisions produce 3 polar bodies that die and 1 egg Polar bodies die because of unequal division of cytoplasm Immature egg called oocyte Starting at puberty, one oocyte matures into an ovum (egg) every 28 days
  35. 35. Oogenesis
  36. 36. Oogenesis Polar body a (haploid) X a Polar Bodies X a (haploid) a X X Mitosis Meiosis I Meiosis II A XOogonium A(diploid) Primary X oocyte A X (diploid) Ovum Mature Secondary A Egg (haploid) oocyte X (haploid) Second polar body (haploid)
  37. 37. CheckpointHow many chromosomes would a sperm or egg contain if either one resulted from the process of mitosis?A: 46 Chromosomes
  38. 38. CheckpointOogenesis results in______. 1. 4 polar bodies 2. 3 polar bodies 3. 1 ovum 4. Both 2 & 3
  39. 39. CheckpointWhy is the sperm so small compared to the egg?A: The egg has all the starting nutrients, organelles and building blocks. The sperm only provides DNA. That is why oogenesis only produces one ‘good’ egg.
  40. 40. Mitosis Meiosis Number of 2 1 divisions Number of 2 4daughter cells Genetically Yes No identical?Chromosome # 46 23 Where Somatic cells Germ cells When Throughout life At sexual maturity Role Growth and repair Sexual reproduction
  41. 41.  STUDENT
  42. 42. MeiosisThe process to make cells with ___________ thenumber of chromosomes for sexual reproductionOccurs in our germ cells that produce gametes ___________ & ______________Results in ____________ cells genetically differentfrom parent cell and from each otherHaploid (____) cells
  43. 43. Why Do We Need Meiosis?It is the fundamental basis of sexual reproductionTwo ____________ (n) gametes are brought togetherthrough fertilization to form a _______________(2n) _______________If egg and sperm had the same number ofchromosomes as other body cells then the offspringwould have too many chromosomes.
  44. 44. Meiosis must ____________ the chromosome number by____________ (n)_____________________ then restores the 2n number from mom from dad child too much! meiosis ____________ genetic content The right number!
  45. 45. Fertilization 2n = ____ n =____
  46. 46. Meiosis-ReplicationReplication is the process ofduplicating a______________________Occurs prior to divisionReplicated copies are calledsister chromatidsHeld together at__________________
  47. 47. Gene Sister Homologous Chromatids chromosomes (same ________, (same _________, same _________)different ________)Homologous chromosomes are the same ________ & ___________Carry genes for the same trait but are _______ identical!
  48. 48. CHECKPOINT √ Meiosis results in ____.1. 4 identical cells 2. 4 genetically different cells3. 2 genetically different cells 4. 2 identical cells Homologous chromosomes are _____. 1. Same in size 2. Same in shape 3. Carry genes for the same trait 4. All of the above Why do we need meiosis?
  49. 49. Sister chromatids separate Homologous chromosomes separate Meiosis I Meiosis II______________ ______________ ______________
  50. 50. Early prophase I Late prophase I Homologous pair. Chromosomes condense. Crossing over occurs. Spindle forms. Nuclear envelope fragments.
  51. 51. Prophase I : Crossing-Over_____________ – the pairing of homologouschromosomes Group of 4 __________________ Homologous chromosomes Join to form a (each with sister chromatids) ________________
  52. 52. Homologouschromosomes in a tetrad____________________each otherPieces of chromosomes orgenes are____________________Produces geneticrecombination in the____________________
  53. 53. Metaphase I Anaphase I Telophase I________________ Homologous Nuclear envelopes________________ chromosomes reassemble.of chromosomes _______________align along the Spindle disappears.equator of the cell Sister chromatids Cytokinesis divides remain attached at cell into ________. the _____________
  54. 54. Meiosis II Only _______ of the homologous pair of chromosome is present in the cell.Gene Z Sister chromatids carry _________________ genetic information. Meiosis II produces _______________ with one copy of each chromosome and thus one copy of each _________.
  55. 55. Prophase II Metaphase II Anaphase IINuclear envelope Chromosomes ________________fragments. align along ________________ ________________ separate and moveSpindle forms. of cell. to opposite poles.
  56. 56. Telophase IINuclear envelope assembles.Chromosomes____________.Spindle disappears.Cytokinesis divides cell into________.
  57. 57. Results of Meiosis _____________(egg & sperm) form Four haploid cells (___) with one copy of each chromosome One ________ of each gene ________________ combinations of alleles for different genes along the chromosome
  58. 58. CHECKPOINT √ Which best describes crossing-over?1. Pieces of genes are exchanged 2. Allow genetic variation3. Occurs in Prophase I 4. All of the above During anaphase what is pulled apart? 1. Centromere 2. Homologous chromosomes 3. Sister chromatids 4. Spindle fibers Which best describes a haploid cell?1. n 2. Half the genetic information3. Gametes 4. All of the above
  59. 59. SpermatogenesisOccurs in the ___________Two divisions produce 4__________________Spermatids mature into__________________Men produce about250,000,000 sperm per day
  60. 60. Spermatid
  61. 61. OogenesisOccurs in the _________________Two divisions produce: _______ __________ bodies that die because of unequal division of cytoplasm _____ egg- Immature egg called _____________Starting at puberty, one oocyte matures into an ovum(egg) every 28 days
  62. 62. CHECKPOINT √How many chromosomes would a sperm or egg contain if either one resulted from the process of mitosis? Oogenesis results in______. 1. 4 polar bodies 2. 3 polar bodies 3. 1 ovum 4. Both 2 & 3 Why is the sperm so small compared to the egg?
  63. 63. Mitosis MeiosisNumber of divisionsNumber of daughter cells Genetically identical? Chromosome # Where When Role

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