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Meiosis

Meiosis. Meiosis – Type of cell division that happens only in sex cells (gametes) The resulting cells receive only half the number of chromosomes present in somatic (body) cells. Meiosis Video. How many chromosomes do human somatic cells have?.

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Meiosis

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  1. Meiosis Meiosis – Type of cell division that happens only in sex cells (gametes) The resulting cells receive only half the number of chromosomes present in somatic (body) cells. Meiosis Video

  2. How many chromosomes do human somatic cells have? • Karyotypes show that human somatic cells have 46 chromosomes and these chromosomes come in pairs.

  3. Human somatic cells are said to be diploid. Diploid – cells having pairs of chromosomes These pairs are said to be homologous. Homologous – similar in structure; the two members of each pair of chromosomes carry DNA with information for corresponding traits.

  4. Why Pairs? Mitosis Mitosis { Fertilization

  5. 46 Mitosis Mitosis { 46 92 92 92 92 92 92 92 Fertilization • This means that the chromosome number has to be 23 to produce gametes (sperm and egg). How is the chromosome number reduced? Meiosis!

  6. Prophase Mitosis vs. Meiosis • Homologous chromosomes pair to form tetrad

  7. Mitosis vs. Meiosis Metaphase • Homologous pairs line up on equatorial plane

  8. Tetrads can be in any order as long as homologous chromosomes are paired Random Assortment

  9. Mitosis vs. Meiosis Anaphase • Homologous chromosomes of each tetrad separate and move to opposite poles

  10. Mitosis vs. Meiosis Telophase • Cytoplasm divides to form two cells.

  11. Mitosis vs. Meiosis Second Stage of Meiosis • Prophase • Chromosomes skip replication • Begin to move toward middle

  12. Mitosis vs. Meiosis • Metaphase • Chromosomes line up on equatorial plate • Spindle fibers attach at centromeres

  13. Mitosis vs. Meiosis • Anaphase • Sister chromatids separate at centromere

  14. Mitosis vs. Meiosis • Telophase • Nuclear membrane reforms. • Chromosome numberis cut in half. Now haploid. Haploid – cells having only one chromosome from each homologous pair.

  15. Differences between Mitosis and Meiosis • Meiosis makes sex cells (gametes) • Meiosis cuts chromosome number in half. No more pairs. • Meiosis has two rounds of cell division while mitosis only has one. • Chromosome pairs (tetrads) meet in the middle during first metaphase.

  16. How many sperm are produced from one cell in meiosis? Four • How many eggs are produced from one cell in meiosis? One

  17. Timing of Meiosis • Females • Begins before birth. • Release one egg a month from puberty until menopause.

  18. Timing of Meiosis • Males • Begins at puberty • Continues until death. Slows down – sperm count lowers.

  19. Terms to be familiar with: • Diploid – cells having two sets of chromosomes; in humans this number is 46 • Haploid – cells having only one chromosome fromm each homologous pair; in humans this number is 23. • Homologous – similar in structure; homologues in diploid cells are the two members of each pair of chromosomes that carry DNA with information for corresponding traits.

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