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Meiosis Chapter 10.2 (Pages 263 – 273)

Meiosis Chapter 10.2 (Pages 263 – 273). Dude, meiosis starts in five minutes . . . I can’t believe you’re not condensed yet http://www.promega.com/. Learning Outcome. Discuss the role of meiosis and sexual reproduction in producing genetic variability in offspring.

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Meiosis Chapter 10.2 (Pages 263 – 273)

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  1. MeiosisChapter 10.2 (Pages 263 – 273) Dude, meiosis starts in five minutes . . . I can’t believe you’re not condensed yet http://www.promega.com/

  2. Learning Outcome • Discuss the role of meiosis and sexual reproduction in producing genetic variability in offspring. • Include: crossing-over, randomness

  3. www.geneticusb.blogfa.com/post-140.aspx http://library.thinkquest.org/28751/review/division/1.html Chromosome Images

  4. Chromosome Images http://hopes.stanford.edu/basics/dna/f_b11homolgs.jpg

  5. http://home.wxs.nl/~gkorthof/images/chromosome_structure.jpg http://faculty.ksu.edu.sa/17257/Pictures%20Library/Forms/DispForm.aspx?ID=5

  6. Meiosis • In complex plants and animals where sexual reproduction occurs, there are two types of cells.

  7. http://www.healthystemcells.org/stemcellbenefits.htm Cell Types • Somatic Cells • These are the cells that make up our bodies (muscles, bones, blood, etc.). • Diploid • These cells reproduce by mitosis.

  8. neurophilosophy.wordpress.com/.../ Cell Types (cont’d) • Reproductive Cells • These cells are specialized for reproducing offspring through sexual reproduction. • The gametes have half the DNA (haploid, single stranded) compared to the regular body cells.

  9. Chromosomes (p 264) • Humans have 23 pairs of chromosomes for 46 chromosomes in each cell nucleus. • These cells are called diploid (“di” means double). • 23 from mom homologous pairs • 23 from dad

  10. Autosomes vs Chromosomes • Twenty-two of these pairs are called autosomes. • The twenty-third pair are the sex chromosomes (determine gender – more on this later).

  11. Autosomes • Reproductive cells have a haploid (means “half” the number of) number of chromosomes. • They contain 23 chromosomes not 23 pair • Sperm – male gamete • Egg – female gamete • (see Fig 10.10 p 266)

  12. Chromosomes (cont’d) • Each pair of homologous chromosomes has genes for the same traits, such as plant height. (not necessarily identical) • These genes are arranged in the same order (see Fig 10.10 p 265) • Do Problem Solving Lab 10.2 p 264

  13. Purpose of Meiosis • If mom gives the baby 46 chromosomes and dad gives the baby 46 chromosomes we HAVE A PROBLEM! • Junior gets 92! Oops! • Moms and dads need a method of making special cells with half the DNA.

  14. Purpose of Meiosis (cont’d) • There must be another form of cell division that allows offspring to have the same number of chromosomes as their parents.

  15. Meiosis has two purposes: • To make gametes with half the normal number of chromosomes (haploid gametes). • To make gametes that have variations in their DNA code.

  16. The first half of Meiosis makes diploid cells into two haploid cells(Meiosis I).

  17. NOTE: • The first half of Meiosis makes diploid cells into two haploid cells(Meiosis I). • Second half of meiosis splits double strands to single strands. • (See Fig 10.12 p 267)

  18. Crossing Over • Some variation is achieved in anaphase 1, but not enough • Further variation is achieved through a process known as Crossing Over.

  19. Crossing Over (cont’d) • The X’mes, in a tetrad (two homologous pairs), pair so tightly that non – sister chromatids from homologous pairs actually break off and exchange genetic material. • This can occur at any location on a chromosome (random).

  20. Crossing Over (cont’d) • It is estimated that there are 2-3 cross-overs in human X’mes during M1. • What happens in one chromosome is completely independent from what happens in another chromosome. • This is what results in so much variation

  21. http://pl-bioblog.blogspot.com/ Crossing Over (cont’d)

  22. AM I really unique? • So how many different gametes can be produced? • How many different offspring can be produced?

  23. “I can’t live without you Martha.” Crossing Over (cont’d) • This process results in endless possibilities because each pair of X’mes can line up one of 2 ways (see p 269-270) • (2n where n = # of X’me prs.)

  24. Crossing Over (cont’d) • Peas with 7 prs. of X’mes (2n = 27 = 128) • Remember, any egg can be fertilized by any sperm • 128 x 128 = 16 384 different possible offspring • Human with 23 prs (2n = 223 = over 8 million) • 223 x 223 = about 70 trillion

  25. Gametogenesis • The formation of gametes from germ cells • Different for sperm and egg cells • Oogenesis vs. spermatogenesis • More about this later

  26. http://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-20/2009.jpghttp://www.mun.ca/biology/desmid/brian/BIOL2060/BIOL2060-20/2009.jpg Gametogenesis

  27. In Summary • Three processes guarantee variation in gamete formation • Independent orientation • Mixing of mom and dad’s x’mes • Crossing over • Random fertilization • GeneticVariation • stage of meiosis • Animation: Unique Features of Meiosis

  28. Activity/Assignment • Read p 266 – 270 and fill in meiosis chart. • Play Dough Meiosis • (MiniLab 10.2 – p268 text & worksheet p3) • Finish heredity key terms

  29. http://gcsebiologyblog.blogspot.com/2008/08/comments-and-questions.htmlhttp://gcsebiologyblog.blogspot.com/2008/08/comments-and-questions.html

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