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Meiosis

I can list, describe and diagram the phases of meiosis. Meiosis. Meiosis. Meiosis results in the formation of haploid cells . In Humans, these are the Ova (egg) and sperm . Ova are produced in the ovaries in females Process is called oogenesis

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Meiosis

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  1. I can list, describe and diagram the phases of meiosis. Meiosis

  2. Meiosis • Meiosis results in the formation of haploid cells. • In Humans, these are the Ova (egg) and sperm. • Ova are produced in the ovaries in females • Process is called oogenesis • Sperm are produced in the testes of males. • Process is called spermatogenesis

  3. Spermatogenesis & Oogenesis

  4. Interphase I • Prior to division (S phase), amount of DNA doubles • Start with 46 (23 pairs) chromosomes • Result: 2 copies of each chromosome • Sister chromatids are attached at centromeres

  5. Prophase I • Longest and most complex phase • Chromosomes condense. • Spindle starts to form. • Nuclear envelope breaks down.

  6. Prophase I (cont) • Synapsis occurs - Homologous chromosomescome togetherto form a tetrad. • Tetrad is two chromosomesor four chromatids. 8

  7. Prophase I (cont) • Crossing over occurs • Segments of nonsisterchromatids break and reattach at similar locations. • Results in new genetic combinations of offspring. • This is the main advantage of sexual reproduction.

  8. Chiasmata • The attachment sites that result from crossing over • Holds homologous chromosomes together until anaphase I

  9. Metaphase I • During Metaphase Itetrads line-up along the metaphase plate or EQUATOR • Chiasmata are still present

  10. Anaphase I • Each HOMOLOGOUS CHROMOSOME is pulled to opposite sides of the cell. • Sister chromatids are still paired

  11. Telophase I and Cytokinesis • Nuclear membrane forms • Two new cells form

  12. Meiosis II • DNA DOES NOT replicate • Chromosomes consist of two replicated sister chromatids Sister chromatids

  13. Prophase II • Same as Prophase in mitosis • Nucleus & nucleolus disappear • Chromosomes condense • Spindle forms

  14. Metaphase II, Anaphase II • Chromosomes align on metaphase plate • SISTER CHROMATIDS separate

  15. Telophase II and Cytokinesis • Nuclei and Nucleoli reform, spindle disappears • CYTOKINESIS occurs. • Remember: FOUR HAPLOID • DAUGHTER cells are produced. • Called GAMETES (eggs and sperm)

  16. Spermatogenesis • Spermatogenesis usually begins at 12-13 years of age and continues throughout life. • Several hundred million sperm cells are produced daily by healthy young adult males. 

  17. Oogenesis • Primary oocytes are found at 5th month of embryogenesis and arrest at Prophase I • Once in puberty, some cells will continue meiosis, but arrest again at metaphase II • Entry of sperm triggers the finish of meiosis

  18. Fertilization

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