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Today…. More Meiosis!

Today…. More Meiosis!. Meiosis I Crossing Over Independent Assortment Meiosis II Meiosis poster project ***Chapter 5 test today at lunch ***. Chapter 6: Meiosis is the basis of Sexual Reproduction. Chapter 6: Meiosis is the basis of sexual reproduction.

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Today…. More Meiosis!

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  1. Today…. More Meiosis! • Meiosis I • Crossing Over • Independent Assortment • Meiosis II • Meiosis poster project ***Chapter 5 test today at lunch***

  2. Chapter 6: Meiosis is the basis ofSexual Reproduction

  3. Chapter 6: Meiosis is the basis of sexual reproduction By the end of section 6.1 you should be able to understand the following: • Meiosis produces gametes with half the number of chromosomes as body cells • Meiosis occurs in two parts, meiosis I and meiosis II • Meiosis I creates variation in organisms through the shuffling of genetic information • Mutations can occur during meiosis and can cause genetic disorders

  4. Chromosomes • Genetic info. is inherited from parents’ chromosomes (wound up DNA + protein) • All normal (body cells) are diploid, meaning they have 2 sets of chromosomes (2n) • Diploid number in humans = 46 (2 x 23 chromosomes) • One set from each parent’s gamete (sperm or egg cell) • Gametes are haploid, meaning they contain only one set of chromosomes, half the diploid number (n) = 23 in humans

  5. Diploid or Haploid? 23 46

  6. Homologous Chromosomes MOM Dad • homologous pairs • Match, but are not identical • (sister chromatids are identical) • same size,contain similar genes(a sequence of DNA that codes for a specific protein) • E.g., gene for eye colour

  7. Sexual Reproduction: Two Parents Needed 23 • Gametes = Specialized reproductive cells (egg and sperm) • MEIOSIS produces haploid gametes • Fertilization = 2 different gametes combine (egg + sperm) 23 46

  8. Meiosis: occurs only in sex cells • A type of cell replication that has 2 divisions and results in 4 gamete cells that have half the original number of chromosomes (haploid) and are genetically different from each other and parent cells. • 2 parts • MEIOSIS I (the first division) • MEIOSIS II (the second division)

  9. Interphase before meiosis 1 • Chromosomes duplicate • Each chromosome forms a pair of chromatids • DIPLOID

  10. Meiosis I (first cell division) • reducesnumber of chromosomes by half (÷ by 2) • 1 member from each homologous pair goes into different cell • produces 2 cells

  11. Meiosis I • Cell goes through same stages of division as in mitosis (PMAT) except… • Homologous chromosomes pair up along equator (metaphase I)

  12. Meiosis II • Similar to mitosis again! • In metaphase II, sister chromatids are separated • produces 4cells (splits the 2 cells from meiosis I) • Result: 4 haploid gamete(daughter) cells produced from one original diploid parent cell

  13. Meiosis Video https://www.youtube.com/watch?v=D1_-mQS_FZ0

  14. meiosis

  15. Events in meiosis that produce variation 1. Crossing over 2. Independent assortment

  16. Crossing over produces variation • Homologous chromosomes pair up in meiosis I • Parts of non-sister chromatids “cross over” each other and exchange DNA segments • Multiple crossovers can occur between 2 chromosomes • Increases genetic possibilities

  17. Independent assortment produces variation • Pairs of chromosomes in meiosis I separate independently • (mom’s or dad’s)

  18. Summary • ________ - produces haploid gametes • _______ reproduction - needs __ parents • Sexual reproduction - requires specialized ________ cells • ________ __ - reduces the number of chromosomes by half • ________ __ - reduces the number of chromatids by half • ________ - results in the production of __ cells with ________ the number of chromosomes

  19. Summary • Meiosis - produces haploid gametes • Sexual reproduction - needs 2 parents • Sexual reproduction - requires specialized gamete cells • Meiosis I- reduces the number of chromosomes by half • Meiosis II - reduces the number of chromatids by half • Meiosis - results in the production of 4 cells with half the number of chromosomes

  20. comparing

  21. Today…. More Meiosis! • Meiosis I • Crossing Over • Independent Assortment • Meiosis II • Meiosis poster project ***Chapter 5 test today at lunch*** Coming up… Problems with Meiosis, WB 82-85

  22. Comparing Meiosis and Mitosis

  23. Comparing Meiosis and Mitosis

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