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Unit 9 lesson 2: Meiosis

Unit 9 lesson 2: Meiosis. https://superchicbio.files.wordpress.com/2015/06/sexual-reproduction-avatar.gif. Common words in today’s notes. gametes (sex cells) s perm e gg h aploid c hromosomes. Meiosis overview. Look at the first two letters of the word meiosis. It spells the word me .

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Unit 9 lesson 2: Meiosis

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  1. Unit 9 lesson 2: Meiosis https://superchicbio.files.wordpress.com/2015/06/sexual-reproduction-avatar.gif

  2. Common words in today’s notes • gametes (sex cells) • sperm • egg • haploid • chromosomes

  3. Meiosis overview • Look at the first two letters of the word meiosis. It spells the word me. • Meiosis is how ME got here! • “Me” got here from sexual reproduction. • Two gametes (one egg and one sperm) came together to make an organism (me!) • Meiosis is the cell division that makes sex cells or gametes.

  4. Meiosis • Cells divide into sex cells (gametes) • Gametes are haploid, or n • Haploid = 1/2 the correct number of chromosomes for organism • Male sex cell • Sperm • Made in testes

  5. Meiosis • Female sex cell • Egg • Made in ovaries • Gametes contain ½ the number of original chromosomes.

  6. Human Chromosome Numbers • Human body cells have 46 chromosomes. • Human sex cells formed from meiosis have 23 chromosomes. • Human sex cells or gametes have ½ the number of chromosomes found in the body cells of an organism.

  7. Overview of Meiosis

  8. Meiosis overview (2)

  9. Meiosis produces 4 new cells from one. • The new cells each contain ½ number of chromosomes. • Notice that no two sex cells are alike! http://www.wereyouwondering.com/what-is-the-difference-between-mitosis-and-meiosis/

  10. Meiosis forms 4 male gametes (sperm) • Meiosis forms 1 egg and 3 smaller cells in female.

  11. Why Meiosis? • Results in sex cells (gametes) for sexual reproduction • Cells made by meiosis contain ½ the number of chromosomes for the organism (23 for humans) • Sex cells or gametes are haploid or have an “n” number of chromosomes

  12. Why Meiosis? • Produces cells with HALF the number of chromosomes so that fertilization can take place • The beginning of the word haploid sounds like the beginning of the word HALF! • Source of variation in organisms • All sperm and egg are different • Chromosomes can “exchange” DNA in a process called crossing over • =Increases variety! • Image: http://www.phschool.com/science/biology_place/labbench/lab3/images/crossovr.gif

  13. Meiosis • What is the second letter in the word meiosis? • It is the letter e. • All of the cells that are formed from meiosis have an e in them! • Sex cells • Gametes • Egg • Sperm • Meiosis happens in ovaries and testes

  14. Let’s Look at Meiosis 2n n n n n n n http://www.phschool.com/science/biology_place/biocoach/meiosis/geneseg1.html

  15. Why is meiosis important? • Meiosis must reduce the number of chromosomes by half for fertilization • In fertilization the egg and sperm come together to make one cell called a zygote. • Fertilization creates a single-celled zygote with the correct number of chromosomes for the organism (46 for humans). • Zygote then grows by mitosis, making body cells.

  16. Fertilization Fertilization egg (n) + sperm (n) http://www.dnalc.org/view/16240-Gallery-8-Sperm-fertilzing-an-egg.html Growth of cells by mitosis Zygote (2n) http://www.americanpregnancy.org/infertility/zift.html http://onepregnancy.files.wordpress.com/2011/02/2cell-embryo.jpg

  17. Let’s Review • Father makes sperm by meiosis • Mother makes eggs by meiosis • Sperm and eggs have ½ the number of chromosomes for an organism Sperm (n) haploid 23 chromosomes Growth by mitosis Zygote (2n) diploid 46 chromosomes Formed by meiosis Fertilization Egg (n) haploid 23 chromosomes

  18. *Notice meiosis starts with 1 cellwith 4 chromosomes http://terra.dadeschools.net/books/Biology/BiologyExploringLife04/0-13-115075-8/text/chapter9/concept9.5.html

  19. *meiosis ends with 4 cells with 2 chromosomes in each http://terra.dadeschools.net/books/Biology/BiologyExploringLife04/0-13-115075-8/text/chapter9/concept9.5.html

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