Meiosisformoodle2013 14-140122101626-phpapp02
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Meiosisformoodle2013 14-140122101626-phpapp02

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  • Figure 8.12A The human life cycle
  • Teaching Tips
    1. If you wish to continue the shoe analogy, crossing over is somewhat like exchanging the shoelaces in a pair of shoes (although this analogy is quite limited). A point to make is that the shoes (chromosomes) before crossing over are what you inherited . . . either from the sperm or the egg; but, as a result of crossing over, you no longer pass along exactly what you inherited. Instead, you pass along a combination of homologous chromosomes (think of shoes with switched shoelaces). Critiquing this limited analogy may also help students to think through the process of crossing over.
    2. In the shoe analogy, after exchanging shoelaces, we have “recombinant shoes”!
    3. Challenge students to consider the number of unique humans that can be formed by the processes of the independent orientation of chromosomes, random fertilization, and crossing over. Without crossing over, we already calculated over 70 trillion possibilities. But as the text notes in Module 8.17, there are typically one to three crossover events for each human chromosome, and these can occur at many different places along the length of the chromosome. The potential number of combinations far exceeds any number that humans can comprehend, representing the truly unique nature of each human being (an important point that delights many students!)
  • Student Misconceptions and Concerns
    Some students might conclude that sex chromosomes function only in determining the sex of the individual. As the authors note, sex chromosomes contain genes not involved in sex determination.
    Teaching Tips
    Students might recall some basic genetics, remembering that for many traits a person receives a separate “signal” from mom and dad. These separate signals for the same trait are carried on the same portion of homologous chromosomes, such as the freckle trait noted in Module 8.11.
  • Figure 8.13_4 The stages of meiosis: Meiosis II
  • Figure 8.12B How meiosis halves chromosome number
  • Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome
  • Figure 8.19A A karyotype showing trisomy 21, and an individual with Down syndrome
  • Student Misconceptions and Concerns
    Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23.
    Teaching Tips
    1. The Human Genome Website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at www.genomics.energy.gov.
    2. Challenge students to create a simple sentence and then modify that sentence to represent (a) a deletion, (b) a duplication, and (c) an inversion as an analogy to these changes to a chromosome.
  • Student Misconceptions and Concerns
    Before addressing karyotyping and nondisjunction events, consider reviewing the general structure and terminology associated with replicated chromosomes and the arrangement of chromosomes during metaphase of mitosis, meiosis I, and meiosis II. Figures 8.3B and 8.14 will be particularly helpful. A firm foundation in chromosome basics is necessary to understand the irregularities discussed in Modules 8.19–8.23.
    Teaching Tips
    1. The Human Genome Website is a tremendous asset for nearly every discussion related to human genetics. It can be accessed at www.genomics.energy.gov.
    2. Some syndromes related to human sexuality are not the result of abnormalities in sex chromosome number. Androgen insensitivity syndrome produces sterile males who possess mostly female sex characteristics. People with this condition are genetically male, but have bodies that fail to respond to male sex hormones. The National Institute of Health web site “Genetics Home Reference” can provide additional details about this and most genetic disorders at http://ghr.nlm.nih.gov/.

Transcript

  • 1.  Organisms receive half of their DNA from each parent  Sperm and eggs cells (haploid) combine to create a zygote (diploid)  Used by most animals, fungi, plants, and algae
  • 2. Haploid gametes (n = 23) A life cycle n Egg cell n Sperm cell Meiosis Ovary Fertilization Testis Diploid zygote (2n = 46) 2n Key Multicellular diploid adults (2n = 46) Mitosis Haploid stage (n) Diploid stage (2n)
  • 3.  Humans body cells are diploid (2N)   2N = 46 Gametes - sex cells Males – sperm  Females – eggs   Gametes are HAPLOID     N = 23 Fertilization restores the diploid state (N + N = 2N) Zygote - a fertilized egg (2N)
  • 4.  What happens during Interphase???  DNA REPLICATION!!! 2N 2N
  • 5.    Occurs in Prophase I Chromosomes exchange portions of their chromatids Increases genetic variation
  • 6. © 2012 Pearson Education, Inc.
  • 7.  Homologous chromosome pair Centromere © 2012 Pearson Education, Inc.
  • 8. 2N • Prophase I – homologous chromosomes form tetrads & crossing over occurs • Metaphase I – tetrads line up along the middle • Anaphase I – homologous chromosomes separate • Telophase I – two nuclei form • Cytokinesis I – cells separate N N
  • 9. • DNA replication DOES NOT occur between Meiosis I & II N • Prophase II – spindle forms, prepares for division N • Metaphase II – chromosomes align along the center • Anaphase II – sister chromatids separate • Telophase II – nuclei reform; cytokinesis N N N N Looks A LOT like MITOSIS!
  • 10. Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis Haploid daughter cells forming
  • 11. SUMMERY OF THE MEIOSIS PROCESS 3
  • 12.   Process to make haploid gametes Chromosome # is cut in half  2N    N Occurs in ovaries & testes TWO cell divisions Increases genetic variation
  • 13. Down syndrome
  • 14. Down syndrome
  • 15.   Men: 4 sperm are made Women: only 1 egg is made
  • 16. Deletion Inversion Duplication Reciprocal translocation Homologous chromosomes © 2012 Pearson Education, Inc. Nonhomologous chromosomes
  • 17. Meiosis vs. Mitosis
  • 18.  In meiosis, “crossing over” occurs during metaphase I.  Chromosomes form tetrads  Homologous chromosomes “swap” parts of their DNA  leads to genetic variation
  • 19.  Mitosis makes cells for growth, development, repair, and asexual reproduction  Meiosis makes cells for sexual reproduction
  • 20.  The following table lists the most common human sex chromosome abnormalities. © 2012 Pearson Education, Inc.
  • 21.     Campbell &Reece,(2010) Biology Williamson, J. LS3AFET . Unit 3. University of Johannesburg: Science Department, 2014. Shilma, S. Meiosis. (2011). http://www.worldstarhiphop.com/videos/vi deo.php?v=wshhk0A758v5lEkmCKrk