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meiosis

meiosis. * Mitosis produces 2 exact copies of “body” cells In meiosis, sex cells (gametes) are produced Body cells are diploid which means they have 2 of each chromosome, or a pair of each chromosomes. {1 from mom, 1 from dad}.

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meiosis

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  1. meiosis

  2. *Mitosis produces 2 exact copies of “body” cells • In meiosis, sex cells (gametes) are produced • Body cells are diploid which means they have 2 of each chromosome, or a pair of each chromosomes. {1 from mom, 1 from dad}

  3. 1. The number of chromosomes in a cell depends on what kind of organism it is. a. Ex. Humans have 46 chromosomes, or 23 pairs.

  4. 2. Homologous chromosomes: chromosomes containing same information a. One from mother & 1 from father; represented as 2n

  5. 3. Haploid cells contain only 1 chromosome of a homologous pair. They are called sex cells or gametes (sperm and egg). a. Represented as n. • Humans: n= 23 • Fruit flies: n= 4

  6. b. Gametes (haploid sex cells) fuse during sexual reproduction to form a diploid zygote. c. Meiosis is the process of forming haploid cells from diploid cells. It has 2 main parts:

  7. C. Meiosis I: 1. Chromosomes have replicated during interphase 2. Matching (or homologous chromosomes) move together, forming a tetrad. One chromosome is from mom and one is from dad. A tetrad is composed of 2 chromosomes each made up by 2 chromatids so has a total of 4 chromatids.

  8. Crossing over occurs when tetrads forms. b. The process where sister chromosomes come together is called synapsis

  9. c. What does crossing over create? -genetic variation:

  10. 3. Nucleoli and nuclear membrane disappears. 4. Spindle fibers forms. 5. Tetrads line up at equator. 6. The homologous chromosomes separate and move to opposite ends.

  11. 7. Cell divides into 2 daughter cells- each still contains a double-stranded chromosome. 8. Divided into: Prophase I Metaphase I Anaphase I Telophase I

  12. D. Meiosis II 1. Chromosomes line up at equator. 2. Centromere splits, and sister chromatids separate.

  13. 3. Each cell separates into 2 daughter cells, so now there are 4 cells, each with a single-stranded chromosome. 4. Divided into Pro II, Meta II, Ana II, Telo II Meiosis – 1

  14. Question Before which stage(s) does DNA replication occur?

  15. E. Cell made during meiosis have to specialized into specific sex cells: Gametogensis F. During spermatogenesis, 4 haploid sperm are produced. During oogenesis, 1 haploid egg is produced and 3 polar bodies are produced. G. Meiosis is sometimes called reductiondivision and is important because it provides for geneticvariation.

  16. Human cells have 23 pairs of chromosomes, meiosis may result in 223 or _____________ possible combinations of chromosomes!!! 8,388,608

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