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Class Objectives:

Class Objectives:.  Distinguish between haploid and diploid cells and its relation to meiosis and fertilization. D istinguish the various phases of meiosis due to the position of the chromosomes at that particular phase.

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Class Objectives:

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  1. Class Objectives: Distinguish between haploid and diploid cells and its relation to meiosis and fertilization. Distinguish the various phases of meiosis due to the position of the chromosomes at that particular phase.  Explain the reason meiosis reduces the number of chromosomes by one half so that when gametes are fertilized the number of chromosomes is restored.  Compare and contrast the cells produced by both mitosis and meiosis and the fate of the cells from each cycle.

  2. Haploid vs. Diploid • Diploid (2n) • A cell with two of each kind of chromosome • ex) somatic cells • Haploid (n) • A cell with one kind of chromosome • ex) germ cells • In mitosis, cells are dividing to form diploid cells • In meiosis, cells are dividing to form haploid cells

  3. The Phases of Meiosis Meiosis I & Meiosis II

  4. Meiosis I • Consists of: • Prophase I • Metaphase I • Anaphase I • Telophase I • Cytokinesis I • Before meiosis begins, what must happen to the cell’s DNA/chromosomes?

  5. Prophase I Like prophase of mitosis: • The nucleus and nuclear envelope disappears. • Centrioles move to the opposite poles and the spindle fibers form between the centrioles. • Chromosomes condenses into sister chromatids. Unlike prophase of mitosis: • Pairs of homologous chromosomes form a tetrad. • Crossing over may occur. • Exchange of genetic material

  6. Metaphase I • Spindle fibers attach to centromeres. • Tetrads line up at the spindle’s equator. Unlike mitosis: • Homologous chromosomes are lined up side by side as tetrads.

  7. Anaphase I • Tetrads, which consist of two homologous chromosomes separate.

  8. Telophase I/Cytokinesis I • The nucleus and nuclear envelope reappears. disappears. • The spindle is broken down and the chromosomes uncoil. • Cytokinesis, the division of the cytoplasm and the organelles begins and ends forming two cells.

  9. Mitosis II • Consists of: • Prophase II • Metaphase II • Anaphase II • Telophase II • The purpose of meiosis II is to separate sister chromatids of each chromosome into separate cells.

  10. Prophase II • The nucleus and nuclear envelope disappear. • Spindle fibers and centrioles form. • Chromosomes condenses into sister chromatids.

  11. Metaphase II • Sister chromatids attach to the centromere. • Sister chromatids line up at the equator.

  12. Anaphase II • Sister chromatids separate into two chromosomes. • Chromosomes move to the opposite poles.

  13. Telophase II/Cytokinesis II • The nucleus and nuclear envelope reforms. • The spindles breakdown. • The cytoplasm divides • 4 haploid cells are formed.

  14. Fertilization • The 4 haploid cells formed in meiosis will become gametes. • Gametes are: • Sperm in males (haploid) • Eggs in females (haploid) • Gametes transmit the genes they contain to their offspring. • When a sperm fertilizes an egg a zygote is formed  this is called sexual reproduction • A zygote is a diploid cell. • Sperm (haploid) + Egg (haploid) = zygote (diploid)

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