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Meiosis: Understanding the Cell Division Process

This text provides a brief overview of the process of meiosis, which is a type of cell division that produces gametes with half the number of chromosomes. It explains the concepts of homologous chromosomes, haploid cells, and crossing over. The text also compares meiosis to mitosis, another type of cell division process.

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Meiosis: Understanding the Cell Division Process

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  1. 11/12/2012 We are going to the lab BRIEFLY today before our QUIZ. You will be in groups of four so begin to plan who you want to work with. Be ready to get started as soon as the bell rings.

  2. 11/12/2012 Pick up notes and glue them onto the next available pages that face each other.

  3. 11/13/2012 Take out your notes from yesterday and be in your seat before the bell rings.

  4. How are sperm and egg made? MEIOSIS

  5. 46 92 46 46 23 23

  6. Homologous Chromosomes • In the body cells (somatic cells) of animals and most plants, chromosomes occur in pairs. • A cell with two of each kind of chromosome is called a diploid cell or 2n. • Organisms produce gametes or sex cells that contain one of each type of chromosome. These gametes are called haploid cells or n. (N represents the number of chromosomes found in each cell.)

  7. Chromosome numbers Do all organisms have the same number of chromosomes?

  8. Homologous Chromosomes • The two chromosomes of each pair in a diploid cell are called homologous chromosomes.

  9. Homologous Chromosomes sex chromosomes autosomes How many autosomes are found in the human body cell? 22 Match up the homologous chromosomes

  10. Meiosis • Meiosis is a two-part cell division process, which results in gametes with one half the number of chromosomes of the parent cell. • produces four daughter cells • all daughter cells are haploid • chromosomes are shuffled in the process, so that each daughter cell has a unique combination (crossing over) http://www.sumanasinc.com/webcontent/anisamples/majorsbiology/meiosis.html

  11. Meiosis creates • 4 haploid cells • Spermatogenesis (meiosis of sperms cells) takes about 64 days. All 4 sperm will survive. • Oogenesis (meiosis of egg cells) is complete when a female is born. Only 1 egg of the 4 will become viable.

  12. Meiosis I 46 In nucleus 92

  13. Meiosis I Now you see them!!!

  14. Meiosis I not a single file line! tetrads = pair of homologous chromosomes

  15. Crossing Over • To make things interesting crossing over can occur. • During Metaphase I, the homologous chromosomes line up together and form tetrads.

  16. Crossing Over • Crossing over: two chromosomes break and reattach to the oppositeend piece. • Crossing over increases the number of variations that can exist in offspring.

  17. Crossing Over • Which of the following did crossing over ONLY take place? B A C

  18. OR Homologs line up at equator or metaphase plate Metaphase I Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION

  19. Meiosis I

  20. Meiosis I 92 46

  21. Meiosis II between What does Inter mean???

  22. Meiosis II

  23. equator Meiosis II NOW … single file line

  24. Meiosis II

  25. MeiosisII 46 23 4 haploid cells

  26. Meiosis I Meiosis II Meiosis – one more time Meiosis is a two-part cell division process….

  27. Meiosis II – one more time … which results in 4gametes with one half the number of chromosomes of the parent cell. 4 haploid cells 4 haploid cells

  28. Mitosis vs. MEIOSIS mitosis meiosis • Creates gametes • 4 cells • haploid cells • 23 chromosomes • Daughter cells are NOT identical to parent cells • 2 divisions • Homologous chromosomes line up in a single file line in metaphase II • Creates somatic cells • 2 cells • diploid cells • 46 chromosomes • Daughter cells are identical to parent cell • 1 division • Homologous chromosomes line up in a single file line in metaphase • Chromosomes duplicate in Interphase • Both a type of cell division • Both required to sustain life http://www.pbs.org/wgbh/nova/miracle/divi_flash.html

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