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Sci 9 Lesson 4 April 6 - Meiosis
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Sci 9 Lesson 4 April 6 - Meiosis

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  • 1. Homework from last class:
    • Complete the Introduction to Meiosis and Reproductive Systems worksheet
    • Study for your Genetics and Reproductive Systems quiz
  • 2. Quiz Time!
    • You have about 10 minutes to write the quiz.
    • Good luck!
  • 3. Chapter 6 pp. 191-197 Ch. 6.1 Meiosis
  • 4. Meiosis
    • Meiosis: the form of cell division that produces gametes (sex cells) with half the number of chromosomes as body cells
    • Diploid (2n)  Haploid (n)
    • parent cell sex cells
    • Meiosis only occurs in gonads (testes or ovaries)
    • Male: spermatogenesis: formation of sperm (spermatozoa)
    • Female: oogenesis : formation of eggs (ova)
  • 5.
    • Meiosis is similar to mitosis , but there are several differences :
    • Involves 2 cell divisions
    • Results in 4 cells with ½ the genetic information
    • (n instead of 2n)
    Meiosis occurs in 2 phases: Meiosis I (1 st cell division) Meiosis II (2 nd cell division) Meiosis I Meiosis II
  • 6. Spermatogenesis & Oogenesis Sperm formation Egg formation Meiosis I Meiosis II Spermatogenesis Oogenesis
  • 7.
    • Meiosis I
    • Prior to meiosis I, DNA replicates once , in interphase
    Fig 6.4 p. 191
  • 8.
    • Meiosis I
    • In meiosis I, a pair of matching homologous chromosomes , one from each parent, lines up at the equator
    • Homologous chromosomes: a pair of matching chromosomes
    Fig 6.5 p. 191
  • 9.
    • Meiosis I
    • Homologous chromosomes line up at the equator
    • The homologous chromosome pair separates and moves to opposite poles of the cell
    • 2 daughter cells result
    Fig 6.5 p. 191
  • 10.
    • Crossing Over
    • Crossing over: event in meiosis I where non-sister chromatids exchange segments of DNA ; results in variation in gametes
    • As a result of crossing over, each chromosome picks up new genetic information from the other
  • 11.
    • Independent Assortment
    • Independent assortment: an event in meiosis I where homologous pairs of chromosomes separate and sort themselves into daughter cells
    • Genes are shuffled  leads to genetic diversity
  • 12.
    • Crossing Over and Independent Assortment
    Fig 6.6A p. 192
  • 13.
    • Meiosis II
    • DNA not replicated again before meiosis II begins
    • Meiosis II is like mitosis (in both processes, the chromatids of each chromosome are pulled to opposite poles
    • Each daughter cell inherits 1 chromatid from each chromosome
    • 4 haploid (n) daughter cells result
    Fig 6.4 p. 191
  • 14.
    • Outcome of Meiosis II
    Fig 6.6B p. 193
  • 15.
    • Summary of Meiosis
  • 16.
    • Meiosis Animation
    • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html
  • 17.
    • Chromosome Mutation in Meiosis
    • Chromosome mutations can occur spontaneously
    • Chromosome mutations  can cause genetic changes
    • Parts of chromosomes can be inverted, deleted, duplicated or moved to another spot (see p. 194)
    Mutagens can cause chromosome mutations
    • Mutagens (ex. radiation, chemicals) can cause chromosome changes
    • Can lead to genetic disease or death
  • 18.
    • Consequences of failed separation of chromosomes in meiosis
    • Failed separation = a gamete may end up with no chromosome or too many copies of a chromosomes .
    • Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic disorders .
    Diagnosing Genetic Disorders The chromosomes of an individual can be studied Karyotype: an image that shows the number of chromosomes a person has; used to diagnose genetic disorders Down syndrome karyotype
  • 19. Homework for next class:
    • Complete Activity 6-1D worksheet (if not completed in class)
    • Complete Check Your Understanding questions 2, 3, 5, 6, 7, 9, 10, 11, 13, 15, 16 (p. 203)
    • Read over class notes and check class blog
    • http://www.msoonscience.blogspot.com
  • 20. Works Cited
    • Images taken from the following sources:
    • http://biologydiva.pbworks.com/w/page/14796955/Chapter-22
    • http://chsweb.lr.k12.nj.us/mstanley/outlines/meiosis/APMeiosis.htm
    • http://www.bcscience.com/bc9/index.html
    • http://geneticssuite.net/node/21
    • http://www.sflorg.com/sciencenews/scn100608_01.html

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