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Unit 7: Cellular Reproduction

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  1. 200 Unit 7: Cellular Reproduction Diploid = 2n Diploid = 2n Formation of sex cells (gametes) Body (somatic) cells divide Ch. 22: Cell Reproduction 22:1 Mitosis & 22:2 Meiosis 2n Meiosis 1 n n haploid = n Meiosis 2 2n 2n n n n n haploid = n

  2. Recall… • Why are cells small? • to keep surface area to volume ratio high • How do cells “stay” small? • by dividing • What must happen before a cell divides? Why? • DNA is replicated so each new cell gets a copy • Why else do cells divide? • growth (increase # of cells) • repair damage • replace old/worn out cells

  3. Cell Reproduction in Prokaryotes • Prokaryotes have a single, circular chromosome. • Cell reproduction is by binary fission. • chromosome duplicates • & cell divides in ½. • Each daughter cell is genetically identical to each other as well as parent cell.

  4. What are the 2 Types of Cellular Reproduction in Eukaryotes? mitosis meiosis occurs in (germ) cells of reproductive organs ovaries & testes cell divides twice results in: 4 haploid cells with ½ # of chromosomes (as parent cell) 23 (humans) function: makes gametes (sperm & eggs) for sex. reprod. promotes variation • occurs in all body (somatic) cells • cell divides once • results in: • 2 diploid cells • with same # of chromosomes (as parent cell) • 46 (23 pairs) (humans) • function: • growth • repair

  5. Diploid & Haploid Cells • What does it mean when a cell is “diploid”? • cell contains two of each (type of) chromosome • & thus 2 sets of genes • 1 from each parent • How do we indicate that a cell is “diploid”? • represented by 2n • ex.humans  2n = 46 • What types of cells are “diploid”? • ex. somatic (body) cells

  6. Diploid & Haploid Cells • What does it mean when a cell is “haploid”? • cell contains one of each (type of) chromosome • & thus 1 set of genes • ½ the original number • How do we indicate that a cell is “haploid”? • represented by n • ex. humans  n = 23 • What types of cells are “haploid”? • ex. gametes (sperm/eggs)

  7. Cellular Reproduction: Mitosis & Meiosis diploid 2n = 4 diploid 2n = 4 formation of sex cells (gametes) body (somatic) cells divide 2n = 4 (double stranded) 2n = 4 (double stranded) n = 2 (double stranded) Meiosis 1 haploid n = 2 n = 2 (double stranded) Meiosis 2 (single stranded) 2n = 4 (single stranded) 2n = 4 (single stranded) haploid n = 2 n = 2 n = 2 n = 2 n = 2

  8. Mitosis (Ch. 22:1)

  9. The Cell Cycle Has 3 Main Phases • Interphase • Mitosis • has 4 parts • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis • IPee MATt, C? cytokinesis C Which takes longer, interphase or mitosis?

  10. What is happening in the cell? life functions are being carried out DNA is in the form of...? chromatin What happens before mitosis begins? DNA replicates forming 2 strands called sister chromatids held together by centromere centrioles duplicate (in animal cells only) A. Before Mitosis: Interphase

  11. B. Mitosis (Prophase—Step 1) Spindle fibers centrioles centrioles centrioles centrioles centrioles centrioles centrioles centrioles Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers Spindle fibers • What happens during prophase? • Double-stranded chromosomes become clearly visible. • Nucleolus & nuclear membrane disintegrate. • (In animals) centrioles move to opposite poles (ends). • Spindle fibers form connecting centrioles.

  12. B. Mitosis (Metaphase—Step 2) • What happens during metaphase? • Chromosomes line up at middle (equator) of cell. • Chromosomes attach to spindle fibers by centromeres.

  13. B. Mitosis (Anaphase—Step 3) • What happens during anaphase? • Centromeres divide. • Sister chromatids are pulled apart (@ centromere) • forming single-stranded chromosomes • Chromosomes move toward opposite poles (away from middle).

  14. B. Mitosis (Telophase—Step 4) • What happens during telophase? • Chromosomes gather at opposite ends of “cells”. • Nuclear membrane reforms • forming 2 new nuclei • Chromosomes unravel back into chromatin form. • Nucleoli reappear • Cytokinesis begins • cleavage furrow forms (animal) • cell plate forms (plant)

  15. C. After Mitosis: Cytokinesis • When does cytokinesis start? • during telophase (but cytokinesis is not a phase of mitosis) • What happens during cytokinesis? • Cytoplasm is divided • by cleavage furrow in animal cells • by cell plate in plant cells • which becomes new cell wall • 2 new diploid cells are formed • & have 2 of each chromosome

  16. So, What is the End Result of Mitosis? • The DNA that was duplicated during interphase is equally divided into 2 new diploid daughter cells • same DNA as parent cell & each other

  17. What stage of the cell cycle is represented by each number? 1 4 2 5 3 Mitosis Animations http://www.sumanasinc.com/webcontent/animations/content/mitosis.html http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__mitosis_and_cytokinesis.html http://www.stolaf.edu/people/giannini/flashanimat/celldivision/crome3.swf http://www.teachersdomain.org/asset/tdc02_vid_dnadivide/

  18. Interphase Cytokinesis Cytoplasm divides forming 2 daughter cells that are identical to the parent cell & each other

  19. What are the 2 Types of Cellular Reproduction in Eukaryotes? mitosis meiosis occurs in (germ) cells of reproductive organs ovaries & testes cell divides twice results in: 4 haploid cells with ½ # of chromosomes (as parent cell) 23 (humans) function: makes gametes (sperm & eggs) for sex. reprod. promotes variation • occurs in all body (somatic) cells • cell divides once • results in: • 2 diploid cells • with same # of chromosomes (as parent cell) • 46 (23 pairs) (humans) • function: • growth • repair

  20. Cellular Reproduction: Mitosis & Meiosis diploid 2n = 4 diploid 2n = 4 formation of sex cells (gametes) body (somatic) cells divide 2n = 4 (double stranded) 2n = 4 (double stranded) n = 2 (double stranded) Meiosis 1 haploid n = 2 n = 2 (double stranded) Meiosis 2 (single stranded) 2n = 4 (single stranded) 2n = 4 (single stranded) haploid n = 2 n = 2 n = 2 n = 2 n = 2

  21. Meiosis: The Production of Gametes (22:2) • What would happen if the # of chromosomes wasn’t reduced by ½ during meiosis? • After fertilization there would be 2x the # of chromosomes • How does meiosis promote genetic variation? • “mixing” DNA from 2 different parents 2n = diploid n = haploid Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid # gametes

  22. Meiosis • Meiosis 2 (separation of sister chromatids… essentially mitosis) • has 4 parts • Prophase 2 • Metaphase 2 • Anaphase 2 • Telophase 2 • Cytokinesis 2 • Interphase • Meiosis 1 (separation of homologous chromosomes) • has 4 parts • Prophase 1 • Metaphase 1 • Anaphase 1 • Telophase 1 • Cytokinesis 1

  23. traits. Different versions of a gene for the same trait are called “alleles”.

  24. A. Before Meiosis: Interphase • What happens during interphase? • Cell is diploid (has 2 of each chromosome) • DNA replicates forming double-stranded chromosomes. • But, the cell is still diploid (2n).

  25. What happens during prophase 1? Nucleolus & nuclear membrane disintegrates. (In animals) centrioles move to opposite poles. Spindle fibers form, connecting centrioles. Homologous chromosomes join (synapsis), forming tetrads (4 chromatids). genes may swap (crossing over) B. Meiosis 1 (Prophase 1—Step 1) 2n

  26. B. Meiosis 1 (Metaphase 1—Step 2) • What happens during metaphase 1? • Spindle fibers attach to chromosomes. • Tetrads line up (double file) @ the middle (equator). • Can have different arrangements (due to independent assortment). • What does this cause? • genetic variability 2n

  27. B. Meiosis 1 (Anaphase 1—Step 3) • What happens during anaphase 1? • Tetrads (pairs of double-stranded homologous chromosomes) separate. • move towards opposite poles 2n

  28. B. Meiosis 1 (Telophase 1—Step 4) • What happens during telophase 1? • Chromosomes gather at opposite ends. • Nuclear membrane reforms around each cluster of chromosomes • forming 2 new haploid (n) nuclei • with 1 of each double-stranded chromosome. • Chromosomes unravel back into chromatin form. • Nucleoli reappear. • Cytokinesis 1 starts. n n

  29. C. After Meiosis 1: Cytokinesis 1 • When does cytokinesis 1 start? • during telophase 1 (but is not a phase of meiosis) • What happens during cytokinesis 1? • Cytoplasm is divided • by cleavage furrow in animal cells. • by cell plate in plant cells • which becomes new cell wall. • 2 new haploid cells are formed • with 1 of each chromosome.

  30. Replication does NOT occur again before meiosis 2. Daughter cells from meiosis 1 stay haploid. Meiosis 2 happens in both daughter cells. Moving From Meiosis 1 to Meiosis 2…

  31. What happens during prophase 2? Nucleolus & nuclear membrane disintegrate. (In animals) centrioles move to opposite poles. Spindle fibers form, connecting centrioles. D. Meiosis 2 (Prophase 2—Step 1) n n

  32. D. Meiosis 2 (Metaphase 2—Step 2) • What happens during metaphase 2? • Spindle fibers attach to chromosomes at centromere. • Double-stranded chromosomes line up (single file) @ equator • so 1 sister chromatid is on each side of equator. n n n n n

  33. D. Meiosis 2 (Anaphase 2—Step 3) • What happens during anaphase 2? • Sister chromatids separate (at centromere) • forming single-stranded chromosomes. • move towards opposite poles n n

  34. D. Meiosis 2 (Telophase 2—Step 4) • What happens during telophase 2? • Chromosomes gather at opposite ends. • Nuclear membrane reforms around each cluster of chromosomes • forming 4 new haploid (n) nuclei • with 1 of each single-stranded chromosome. • Chromosomes unravel back into chromatin form. • Nucleoli reappear. • Cytokinesis 2 starts.

  35. E. After Meiosis 2: Cytokinesis 2 n • When does cytokinesis 2 start? • During telophase 2 • What happens during cytokinesis 2? • cytoplasm is divided • by cleavage furrow in animal cells. • by cell plate in plant cells • which becomes new cell wall. • What does each new cell end up with? • combo of chromosomes from mom & dad • Only one chromosome from each homologous pair n n n

  36. To summarize… • Meiosis Has 2 Stages (Divisions)… • Meiosis 1 • Homologous chromosomes are separated, but are still double stranded. • Cells become haploid. • Meiosis 2 • Sister chromatids are separated. • Still haploid, but now have single strands.

  37. End Result of Meiosis • What is the result of meiosis in males? • spermatogenesis (formation of sperm) • all 4 daughter cells become sperm • What is the result of meiosis in females? • Oogenesis (formation of eggs) • only 1 daughter cell becomes ovum (egg) • other 3 daughter cells are small, nonfunctional polar bodies

  38. spermatogenesis

  39. oogenesis

  40. Fertilization • What is fertilization? • the fusion of sperm & egg • What is formed by fertilization? • a zygote (which will develop into a baby) • What happens to the chromosome # after fertilization? • diploid number restored (zygote has 2 of each chromosome) 2n = diploid n = haploid Through meiosis, the chromosome # is reduced to ½ the diploid (2n) #, resulting in the n or haploid # gametes

  41. Review & Animations • mitosis • http://www.biology.arizona.edu/cell_bio/tutorials/cell_cycle/cells3.html • http://www.johnkyrk.com/mitosis.html • http://www.accessexcellence.org/RC/VL/GG/mitosis.php • meiosis • http://www.sumanasinc.com/webcontent/animations/content/meiosis.html • http://www.stolaf.edu/people/giannini/flashanimat/celldivision/meiosis.swf • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__stages_of_meiosis.html • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter28/animation__how_meiosis_works.html • comparison mitosis & meiosis • http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__comparison_of_meiosis_and_mitosis__quiz_1_.html • http://www.pbs.org/wgbh/nova/miracle/divi_flash.html