Meiosis notes


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Meiosis notes

  1. 1. Copy the questions & use 10.1 p. 270 to answer them. <ul><li>What are chromosomes made of? </li></ul><ul><li>What is a gene? </li></ul><ul><li>Draw a pair of homologous chromosomes. </li></ul><ul><li>Answer these after we finish taking notes: </li></ul><ul><li>Compute the number of chromosomes that the gametes of a cat (2n=38 chromosomes) will have. Show work. </li></ul><ul><li>Compare/contrast Telophase I and II. </li></ul>
  2. 2. Chromosomes and Chromosome Number <ul><li>Human body cells have 46 chromosomes </li></ul><ul><li>Each parent contributes 23 chromosomes </li></ul><ul><li>Homologous chromosome -one of two paired chromosomes, one from each parent </li></ul>
  3. 3. Homologous Chromosomes <ul><li>Same length </li></ul><ul><li>Same centromere position </li></ul><ul><li>Carry genes that control the same inherited traits </li></ul><ul><li>One came from Dad, & </li></ul><ul><li>one came from Mom! </li></ul>
  4. 4. <ul><li>An organism produces gametes to maintain the same number of chromosomes from generation to generation. </li></ul>
  5. 5. Compare diploid and haploid number <ul><li>Diploid: cell that contains two of each kind of chromosome (2N) </li></ul><ul><li>Body cells(somatic cells) are diploid </li></ul><ul><li>Haploid: cell with only one kind of chromosome (N) </li></ul><ul><li>Gametes (sex cells) are haploid </li></ul>
  6. 6. Meiosis I <ul><li>The sexual life cycle in animals involves meiosis. </li></ul><ul><li>Meiosis produces </li></ul><ul><li>gametes. </li></ul><ul><li>When gametes </li></ul><ul><li>combine in fertilization, </li></ul><ul><li>the number of </li></ul><ul><li>chromosomes is restored. </li></ul>
  7. 7. Meiosis I <ul><li>Prophase I </li></ul><ul><li>each chromosome pairs with its corresponding homologous chromosome to form a tetrad(4 chromatids) </li></ul><ul><li>The nuclear envelope breaks down. </li></ul><ul><li>Spindles form. </li></ul><ul><li>** Crossing-over- chromosomes will switch some genes. (genetic variation) </li></ul>
  8. 8. Crossing Over
  9. 9. <ul><li>Metaphase I </li></ul><ul><li>Homologous pairs of chromosomes line up together at the middle of the cell </li></ul><ul><li>Chromosome centromeres attach to spindle fibers. </li></ul>
  10. 10. <ul><li>Anaphase I </li></ul><ul><li>homologous chromosomes separate & move to opposite ends (centromeres do not split) </li></ul>
  11. 11. <ul><li>Telophase I & Cytokinesis </li></ul><ul><li>spindle disappears and the cell divides </li></ul>Meiosis I results in 2 haploid(1N) daughter cells, each with half the number of chromosomes as the original cell.
  12. 12. Meiosis II During the second meiotic division, doubled chromosomes will be separated much like they were in mitosis.
  13. 13. Prophase II the spindle apparatus forms and the chromosomes condense
  14. 14. <ul><li>Metaphase II </li></ul><ul><li>a haploid number of chromosomes line up at the equator ( middle ) </li></ul>
  15. 15. <ul><li>Anaphase II </li></ul><ul><li>sister chromatids are pulled apart at the centromere & move to opposite poles </li></ul>
  16. 16. <ul><li>Telophase II (includes cytokinesis) </li></ul><ul><li>chromosomes reach the poles and the nuclear membrane and nuclei reform </li></ul><ul><li>4 new daughter cells are produced </li></ul><ul><li>each new daughter cell has the haploid number of chromosomes </li></ul>
  17. 17. Differences: <ul><li>In females: </li></ul><ul><li>1 mature egg, 3 polar bodies which break down </li></ul><ul><li>Women born with all eggs they will have, meiosis I occurs before birth, meiosis II occurs once a month </li></ul><ul><li>Much larger (egg) </li></ul><ul><li>Have all X chromosomes </li></ul><ul><li>Has no method of movement </li></ul><ul><li>Occurs in ovaries </li></ul><ul><li>oogenesis </li></ul><ul><li>In males: </li></ul><ul><li>4 mature sperm </li></ul><ul><li>Males begin to produce sperm after puberty, produced constantly until death; meiosis II occurs immediately after meiosis I </li></ul><ul><li>Much smaller than egg </li></ul><ul><li>May have X or Y chromosomes </li></ul><ul><li>Have flagella to move </li></ul><ul><li>Occurs in testes </li></ul><ul><li>spermatogenesis </li></ul>
  18. 18. Meiosis/gamete production <ul><li>Females have XX for last pair of chromosomes </li></ul><ul><li>Males have XY for last pair </li></ul><ul><li>Since all eggs are X, father determines the sex of the child since the sperm may be X or Y </li></ul>