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Meiosis & Variation Notes

Meiosis & Variation Notes. Obj. 1 : Define Meiosis and explain its benefits. Obj. 3: Describe 2 ways meiosis causes genetic variation in organisms. Obj. 4 : Explain the importance of genetic variation. Meiosis.

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Meiosis & Variation Notes

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  1. Meiosis & Variation Notes Obj. 1: Define Meiosis and explain its benefits. Obj. 3: Describe 2 ways meiosis causes genetic variation in organisms. Obj. 4: Explain the importance of genetic variation.

  2. Meiosis • Meiosis: a special kind of cell division that forms 4 sex cells (gametes), each with half the number of chromosomes as the parent cell.

  3. Benefits of Meiosis • Variation • Keep number of chromosomes constant after fertilization.

  4. Terms to Know: 1. Gamete: sex cells (egg or sperm) 2. Diploid: any cell that contains 2 complete sets of chromosomes (body cells; 2n=46) 3. Haploid: any cell that contains 1 complete set of chromosomes (gametes; n=23) 4. Homologous chromosomes: a pair of chromosomes, each with the same type and number of genes; one is maternal, one is paternal 5. Phenotype: physical characteristics

  5. If meiosis did not occur, the number of chromosomes would double with each new generation.

  6. Variation Variation: Differences among members of the same population. • Examples: height, color of hair, length of beaks, etc.

  7. Variation • Key to a population’s survival in a changing environment. • As the degree of variation in a population increases, so does the likelihood that the species will survive. Diversity (Variety) = Stability • Organisms that reproduce sexually have much more variation than those that reproduce asexually.

  8. 2 Ways that Meiosis Causes Genetic Variation • Crossing Over: • Occurs at the Prophase I of Meiosis I. • Genes are exchanged between pairs of homologous chromosomes.

  9. 2 Ways that Meiosis Causes Genetic Variation 2. Independent Assortment: • Occurs during Metaphase I of Meiosis I, when the chromosomes line up in the middle. • Maternal and paternal chromosomes line up randomly and independently of each other.

  10. Phases of Meiosis • Objective 2: Describe and order major events of meiosis.

  11. Interphase • Normal Cell Activities • DNA replication

  12. Prophase 1 of Meiosis 1 • Homologous (duplicated) chromosomes condense and pair up • Nuclear membrane dissolves • Crossing over occurs

  13. Metaphase 1 of Meiosis 1 • Homologous chromosomes line up in the middle of the cell – next to their pair • Random/Independent assortment

  14. Anaphase 1 of Meiosis 1 • Homologous Chromosomes separate and move to opposite sides of the cell

  15. Telophase 1 of Meiosis 1 • Membrane pinches in and Cytokenesis occurs – forming 2 haploid cells

  16. Prophase 2 of Meiosis 2 • Duplicated chromosomes re-condense

  17. Metaphase 2 of Meiosis 2 • Duplicated chromosomes line up in the middle of the cell.

  18. Anaphase 2 of Meiosis 2 • Duplicated chromosomes split and move to opposite sides of the cell.

  19. Telophase 2 of Meiosis 2 • Membrane pinches in and Cytokenesis occurs – forming 4 haploid cells

  20. Summary of DivisionsCytokinesis: Division of cytoplam, forming 4 haploid cells1 Diploid Cell  2 Haploid Cells 4 Haploid Cells*DNA replication DOES NOT occur between Meiosis I and Meiosis II!

  21. Mitosis vs Meiosis: The Showdown

  22. Mitosis vs Meiosis: The Showdown

  23. Mitosis vs Meiosis: The Showdown

  24. Mitosis vs Meiosis: The Showdown

  25. Mitosis vs Meiosis: The Showdown

  26. Mitosis vs Meiosis: The Showdown

  27. Mitosis vs Meiosis(continued)

  28. Mitosis vsMeiosis

  29. Mitosis vsMeiosis

  30. Mitosis vsMeiosis

  31. Mitosis vsMeiosis

  32. Mitosis vsMeiosis

  33. NOTES:Human Chromosome Abnormalities & Karyotyping

  34. Chromosome numbers

  35. Chromosomes Karyotype: • ordered display of an individual’s chromosomes. • Collection of chromosomes from mitotic cells. • Staining can reveal visible band patterns, gross anomalies.

  36. Karyotyping

  37. Types of Chromosomal Disorders

  38. Chromosomal Abnormalities: • Changes in structure: • large segments of chromosomes changed • Deletions, Duplications, Inversions, Additions, Translocations • Changes in number: • too many or too few of a certain chromosome • Monosomy (1), Trisomy(3) • Can involve autosomes OR Sex Chromosomes

  39. Chromosomal Abnormalities:Changes in structure

  40. Deletion = piece missing

  41. Cri du chat Syndrome. Partial deletion of short arm of chromosome 5.

  42. Duplication = doubled piece

  43. Addition = piece of extra DNA (viral or other) added

  44. Inversion = sections reversed

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