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Sexual Reproduction & Meiosis

Sexual Reproduction & Meiosis. Sexual Reproduction. During Sexual Reproduction , two sex cells (sperm & egg) come together Sperm are formed in male reproductive organs Eggs are formed in female reproductive organs The joining of egg and sperm is called Fertilization

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Sexual Reproduction & Meiosis

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  1. Sexual Reproduction & Meiosis

  2. Sexual Reproduction • During Sexual Reproduction, two sex cells (sperm & egg) come together • Sperm are formed in male reproductive organs • Eggs are formed in female reproductive organs • The joining of egg and sperm is called Fertilization • The new cell that is formed is called a Zygote

  3. Diploid Cells • Your body forms two types of cells • Body Cells & Sex Cells • A human body cell has 46 chromosomes • Each chromosome has a “mate” that is similar in size and has similar DNA • The “mates” are paired into 23 pairs • When cells have pairs of similar chromosomes they are called diploid.

  4. Haploid cells • Sex cells do NOT have pairs of chromosomes • Human sex cells have 23 chromosomes • They are called haploid

  5. Meiosis and Sex Cells • A process called meiosis produces haploid sex cells • During meiosis, two divisions of the nucleus occur • Meiosis I • Meiosis II

  6. Meiosis

  7. Meiosis i • Before the start of meiosis I, the chromosomes are duplicated just like mitosis • Each set of duplicated chromosomes is called a chromatid

  8. Meiosis I • In Prophase I the chromatids are tightly coiled together, each duplicated chromosome comes near its mate. • What are chromatids?

  9. Meiosis I • In Metaphase I, the pairs of duplicated chromosomes, or chromatids, line up at the equator. Each chromatid pair attaches to a _spindle at the centromere. • What is a centromere?

  10. Homologous Chromosomes

  11. Meiosis I • In Anaphase I the chromosome pairs are pulled to _opposite_sides of the cell. Each duplicated chromosome still has two _chromatids_.

  12. Meiosis I • In Telophase I the _cytoplasm divides and two new cells form. Each cell has one duplicated chromosome from each pair.

  13. Meiosis II • NO chromosome duplication occurs before meiosis II • The two cells formed during meiosis I will begin meiosis II

  14. Meiosis II • In Prophase II the __chromosomes__ and __spindle reappear in each of the cells • In Metaphase II the chromatid pairs move to the equator. • Where is the equator? • However, each centromere attaches to the spindleindividually.

  15. Meiosis II • In Anaphase II the __centromere divides and the _chromatids___ separate and move to opposite sides of the cell. Each _chromatid is now an individual chromosome.

  16. Meiosis II • In Telophase II the spindle disappears and the nuclear membrane forms. The cytoplasm divides and produces __4_ cells.

  17. Summary of meiosis • During meiosis I, two cells formed • During meiosis II, both of these cells formed two cells • Four sex cells were formed • Each sex cell has ½ the number of chromosomes that was in the original nucleus = 4 sex cells with 23 unpaired chromosomes

  18. ZDONK • Donkey (62 chromosomes) + Zebra(46 chromosomes) = Zonkey • How many chromosomes does the Zdonk have? • What happens when meiosis occurs in the Zdonk?

  19. Mistakes in Meiosis • Mistakes in meiosis can produce sex cells with too many or too few chromosomes • If the zygote survives, every cells in that organism will have the wrong number of chromosomes

  20. Down Syndrome (Trisomy 21)

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