Meiosis: (Fig. 7-1) Chp. 7 (pp. 140-157) - PowerPoint PPT Presentation

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Meiosis: (Fig. 7-1) Chp. 7 (pp. 140-157)

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Meiosis: (Fig. 7-1) Chp. 7 (pp. 140-157) Production of sex cells 1/2 the number of chromosomes Gametes-reproductive cells Link!-video Stem Cells A cell that can ... – PowerPoint PPT presentation

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Title: Meiosis: (Fig. 7-1) Chp. 7 (pp. 140-157)


1
Meiosis (Fig. 7-1)Chp. 7 (pp. 140-157)
  • Production of sex cells
  • 1/2 the number of chromosomes

2
Link!-video
Gametes-reproductive cells
3
Stem Cells
  • A cell that can differentiate to become a
    specific type of cell
  • Stem Cells become cells that can do mitosis or
    meiosis

4
Definitions for Meiosis
  • Homologous Chromosomes-
  • Chromosomes that are similar in size, shape and
    content
  • Crossing Over-
  • Portions of one chromatid are
  • shared with a chromatid on
  • another (Homologous
  • Chromosome)
  • - Occurs during meiosis

5
Definitions for Meiosis
  • Haploid- containing one set of chromosomes
  • 23 for humans (sex cells)
  • Diploid- containing two sets of chromosomes
  • Zygote- fertilized egg
  • 46 chromosomes in humans
  • 78 chromosomes in dogs
  • Some plants have thousands

6
Meiosis contributes to Diversity
  • Asexual Reproduction- a single parent passes
    copies of all of its genes to each of its
    offspring. (Clones- not diverse)
  • Ex Binary Fission
  • MORE GENETIC VARIATION MORE DIVERSITY
  • Sexual Reproduction- two parents, each donating a
    haploid reproductive cell
  • IMPORTANT for increasing diversity

7
More diversity added by
  • Mutations- a change in the nucleotide sequence of
    a gene.
  • substitution of bases (A replaced by C)
  • adding bases (A added to gene)
  • deleting bases (A removed from gene)

8
Prophase 1
  • The chromosomes become visible
  • Nuclear envelope breaks down

9
Metaphase 1
  • Pairs of homologous chromosomes move to the
    equator of the cell

10
Anaphase 1
  • Homologous chromosomes move to opposite poles of
    cell

11
Telophase 1
  • Chromosomes gather at the poles of the cell
  • Cytoplasm divides

12
Prophase 2
  • A new spindle forms around the chromosomes

13
Metaphase 2
  • Chromosomes line up at the equator

14
Anaphase 2
  • Centromeres divide.
  • Chromatids are now called chromosomes
  • Chromosomes move to opposite poles of the cell.

15
Telophase 2
  • Cells begin split
  • Cell membrane forms between cells
  • Four gamettes are formed

16
Comparison of Mitosis and Meiosis
17
46 Chromosomes (Diploid)-23 pairs
18
Trisomy 21 or Downs Syndrome
Extra Chromosome
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