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Ponder This…

Ponder This…. If all the cells made by your mother are the same & If all the cells made by your father are the same… Why don’t you and your siblings look exactly the same?. sperm (father). 92?. egg (mother). 46. 46. Ponder This….

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Ponder This…

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  1. Ponder This… If all the cells made by your mother are the same & If all the cells made by your father are the same… Why don’t you and your siblings look exactly the same?

  2. sperm (father) 92? egg (mother) 46 46 Ponder This… If a new human is created from the union of two cells (one from mother and one from the father)… How do you avoid doubling the chromosome number each time reproduction occurs? zygote (fertilized egg cell)

  3. Explanation: • They contain halfthe normal number of chromosomes than a somatic (body) cell, • They are called sex cells (gametes), • They are geneticallyunique, and • They are produced by meiosis, not mitosis. The cells used to make offspring are very different from every other cell in the body.

  4. A Closer Look For example, in the fruit fly, a somatic (body) cell contains 8 total chromosomes. Four chromosomes came from the mother in an EGG cell, and four came from the father in a SPERM cell. Homologous Chromosomes (one maternal and one paternal)

  5. sperm (father) 46 egg (mother) 23 23 Meiosis Produces Sex Cells Egg and sperm cells have ½ as many chromosomes as any body cell. This means that egg and sperm cells have only ONE chromosome from each homologous pair. zygote (fertilized egg cell)

  6. Mitosis vs. Meiosis Mitosis: starts with a diploid cell and produces 2 genetically identical diploid daughter cells. Genetic information remains the same. Meiosis: starts with a diploid cell and produces 4 genetically unique haploid daughter cells. Genetic information is shuffled around.

  7. Phases of MEIOSIS Interphase Events are identical to interphase before mitosis.

  8. Prophase I Crossing Over Occurs #3) Exchange genetic info #2) Form tetrads or a “synapsis” #1) Homologous chromosomes pair up *More variation*

  9. Metaphase I Homologous chromosomes line up at equator in PAIRS.

  10. Anaphase I Homologous chromosomes separate and move to poles.

  11. Telophase I Chromosomes begin to uncoil into chromatin

  12. Interkinesis -Same as Interphase except NO DNA replication

  13. Prophase II

  14. Metaphase II

  15. Anaphase II Chromosomes now break at the centromere.

  16. Telophase II Chromosomes begin to uncoil into chromatin

  17. Interphase *End Result of Meiosis: Four haploid gametes (4 daughter cells) that are genetically unique

  18. Meiosis in Males = Spermatogenesis 23 chromosomes (in humans) Produces four equally sized sperm per starting cell. Begins in puberty and continues every moment of every day throughout life.

  19. Meiosis in Females = Oogenesis egg cell polar bodies Produces one large EGG and 3 small polar bodies per starting cell. Large egg results from an unequal division of cytoplasm during meiosis. This keeps almost all nutrients and organelles in the egg to ensure proper development if fertilization occurs. Females are born with all egg cells “frozen” in prophase I. Eggs mature on a cycle (menstrual cycle). Eggs eventually run out (menopause).

  20. What makes sex cells genetically unique? Half of the chromosomes are randomly placed in each sex cell. Each time a sex cell is made, it has a different combination of chromosomes.

  21. What ELSE makes sex cells genetically unique? crossing over

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