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II. Sexual Reproduction & Meiosis

II. Sexual Reproduction & Meiosis. By Addy Lundberg John Swett High School Crockett, CA. A. Sexual Reproduction. 1. Asexual repro. needs only one parent 2. Sexual repro. needs two sex cells a. Sperm--male sex cell b. Egg--female sex cell. B. Importance of Sex Cells.

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II. Sexual Reproduction & Meiosis

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  1. II. Sexual Reproduction & Meiosis By Addy Lundberg John Swett High School Crockett, CA

  2. A. Sexual Reproduction • 1. Asexual repro. needs only one parent • 2. Sexual repro. needs two sex cells • a. Sperm--male sex cell • b. Egg--female sex cell

  3. B. Importance of Sex Cells • 1. In body cells, chromosomes found in pairs • a. Pairs form because chromosomes are alike • b. Cell with 2 of every kind of chromosome is diploid • c. Sex cell is haploid--23 in egg or sperm

  4. B. Importance of Sex Cells • 2. Sexual repro starts with cex cell & ends with fertilization • a. Zygote is formed--in human now is diploid or 2n with 46 chromosomes

  5. C. Meiosis--Sex Cell Formation • 1. In meiosis, there are 2 divisions of the nucleus: meiosis I & meiosis II • 2. Prophase I: double stranded c’somes and spindle fibers appear; nuclear membrane and nucleolus fade

  6. 3. Metaphase I: chromosome pairs (chromatids) line up spindle fibers attach to centromeres and centrioles 4. Anaphase I: chromotids separate from matching pair

  7. 5. Telophase I: cytoplasm divides and 2 cells form

  8. 6. Prophase II: chromatids and spindle fibers reappear

  9. 7. Metaphase II: chromatids line up in the center of the cell • spindle fibers attach to centromere & centriole • 8. Anaphase II: centromere divides • chromosomes split and move to opposite poles

  10. 9. Telophase II: spindle fibers disappear • nuclear membrane forms around chromosomes at each end of cell • each nucleus has half the # of chromosomes as the original (haploid) • now there are 4 sex cells (daughter cells)

  11. Diploid (2n)

  12. Haploid (n)

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