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Chapter 10 - PowerPoint PPT Presentation


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Chapter 10. Meiosis and Sexual Reproduction. Sexual reproduction. Genes—sequences of DNA in chromosome All genes the same = clone, twins. Sexual reproduction. Meiosis Gamete formation Fertilization. Sexual reproduction. Allele—different forms of the same gene

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chapter 10

Chapter 10

Meiosis and Sexual Reproduction

sexual reproduction
Sexual reproduction
  • Genes—sequences of DNA in chromosome
  • All genes the same = clone, twins
sexual reproduction1
Sexual reproduction
  • Meiosis
  • Gamete formation
  • Fertilization
sexual reproduction2
Sexual reproduction
  • Allele—different forms of the same gene
    • Affects different traits— “dimple”, “no-dimple”
    • Mixing alleles results in variations of traits
chromosomes
Chromosomes
  • Chromosome number—sum total of chromosomes
  • Diploid number—number of chromosomes when including pairs, “2n”
  • Homologous chromosomes—each chromosome in a matched pair
  • Haploid number—half of the normal chromosome number, “n”
chromosomes1
Chromosomes
  • Diploid number = 46 (“2n”)
  • Haploid number = 23 (“n”)

Homologous

Chromosomes

chromosomes2
Chromosomes
  • Duplicated during S-phase of Interphase
  • Divide during anaphase
mitosis
Mitosis
  • During interphase, chromosomes double
  • Cell divides once
  • Chromatid divides once
  • Leaves 2n in each daughter cell
meiosis
meiosis
  • Almost identical to mitosis
  • Chromosomes mix
  • Cells and chromosomes divide TWICE before process ends
  • Ends with 4 daughter cells, each haploid
  • Pro-, Meta-, Ana-, Telophase I
  • Pro-, Meta-, Ana-, Telophase II
meiosis1
Meiosis
  • Prophase 1
    • Homologous chromosomes pair up (Synapsis)
    • Usually swap segments (crossing over)
    • Otherwise normal prophase
meiosis2
Meiosis
  • Metaphase 1
    • Spindle fibers attach to centromere of each type of chromosome
    • Otherwise normal metaphase
  • Anaphase 1
    • Homologous chromosomes separated to each pole of cell
    • Otherwise normal anaphase
  • Telophase 1
    • Cytokinesis (normal telophase)
    • Does NOT go to Interphase
meiosis3
Meiosis
  • Prophase II
    • New centrioles move to poles of new cells
  • Metaphase II
    • Spindle fibers attach to centromeres
    • Chromosomes line in middle
  • Anaphase II
    • Sister chromatids break apart, move to poles
  • Telophase II
    • Cytokinesis
    • Each daughter cell is haploid
meiosis4
Meiosis
  • Several Good animations w/ narration
  • Animation w/ narration, same style as mitosis
mitosis vs meiosis1
Mitosis vs. meiosis
  • Somatic cells
  • Grow, replace, repair
  • 2 daughter cells, 2n
  • No synapsis
  • No genetic diversity
  • One division
  • Sex cells
  • Reproduction
  • 4 daughter cells, n
  • Frequent synapsis
  • Great genetic diversity
  • Two divisions

MITOSIS

MEIOSIS

genetic variation
Genetic variation
  • Crossover (Prophase I)—Switches alleles
  • Homologous Alignments (Metaphase I)
genetic variation humans
Genetic variation--humans
  • 8,388,608 combinations of homologous chromosomes
  • 70,368,744,000,000 possible variations of offspring
  • Including crossing over-- 4,951,760,200,000,000,000,000,000,000 possible variations!!!!!
gametes plants
Gametes--Plants
  • MeiosisSporesMitosisGametophytesFertilization
gametes animals
Gametes--animals
  • Spermatogenesis
    • Primary spermatocyte (2n=46) 2 secondary spermatocytes (n=23)
    • 2 secondary spermatocytes  4 spermatids (n)
    • Spermatids  sperm
gametes animals1
Gametes--animals
  • Oogenesis
    • Primary oocyte (2n)  1 secondary oocyte (n) & 1 polar body (n)
      • Happens before female is born!!!
    • Secondary oocyte (n)  Metaphase II
      • Stops meiosis II here
    • Fertilization of metaphase II oocyte  1 ovum & 1 polar body