Meiosis for moodle
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Meiosis for moodle

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    Meiosis for moodle Meiosis for moodle Presentation Transcript

    • Meiosis STS Biology Unit 4 Genetics Chapter 11
    • Chromosome Number
    • Chromosome Number
      • Eukaryotic cells have pairs of homologous chromosomes
      • Cells with a double set of chromosomes are diploid (2n)
      • Cells with one set of chromosomes are haploid (n)
      • 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)
    • Meiosis…bottom line
      • Process to make haploid gametes
      • Chromosome # is cut in half
        • 2N  N
      • Occurs in ovaries & testes
      • TWO cell divisions
      • Increases genetic variation
    • Prior to Meiosis….INTERPHASE
      • What happens during Interphase???
        • DNA REPLICATION!!!
      2N 2N
    • Meiosis I
      • 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
      2N N N
    • Crossing Over
      • Occurs in Prophase I
      • Chromosomes exchange portions of their chromatids
      • Increases genetic variation
    • Meiosis II
      • Prophase II – spindle forms, prepares for division
      • DNA replication DOES NOT occur between Meiosis I & II
      • Metaphase II – chromosomes align along the center
      • Anaphase II – sister chromatids separate
      • Telophase II – nuclei reform; cytokinesis
      N N N N N N Looks A LOT like MITOSIS!
    • Meiosis in Men vs. Women
      • Men: 4 sperm are made
      • Women: only 1 egg is made
    • Meiosis vs. Mitosis
    • Independent Assortment
      • Mendel’s Law of Independent Assortment
      • Alleles (form of a gene) separate independently of each other
      • Leads to the formation of MANY different gametes
    • Meiosis Summary
      • Chromosome number is cut in half!
      • Produces haploid gamete cells – egg and sperm
      • Tetrads form during Prophase I
        • Crossing over occurs in tetrad formation – leads to increased genetic variation
      • Two cell divisions, but DNA does not replicate between divisions
      • Results in 4 sperm cells in men and 1 egg in women
      • Which chromosomes wind up in which sex cells? It’s random…due to independent assortment!!