Cell division

1. Cell division

2. Chromosomes • Made of DNA • Carries cell genetic information • 23 pair • Differs for different organisms • fruit fly: 8 • Carrot: 18

3. chromosomes • Before a cell can divide it must duplicate DNA • Each chromosome consists of identical sister chromatids • Since they are identical, where will each one go? • One goes to each new cell • Each pair of chromatids are attached at centromere • Usually located near the middle of chromosome

5. Cell cycle • Series of events that cells undergo as they grow and divide • During cell cycle the cell: • Grows • Prepares for division • Divides to form 2 daughter cells, each of which will re-enter into cell cycle

6. Cell cycle • Interphase: “in-between” period of growth • Time spent Between divisions • Cycle consists of 3 phases: • G1 • S • G2

7. Cell cycle: G1 (growth) • Most of the growing • Synthesize proteins

8. Cell cycle: S phase • Chromosomes get replicated • Synthesis of DNA • When completed, cell completes remainder of cycle

9. Cell cycle: G2 • Shortest of phases • Cells prepare for division • Organelles reproduced • Molecules needed for replication created

10. Mitosis • Mitosis: process in cell division where nucleus divides • Divided into 4 stages • Prophase • Metaphase • Anaphase • Telophase

11. prophase • First and longest phase • Chromosomes become visible • Centrioles separate and move to poles • Centrioles help organize mitoticspindle (spindleapparatus): fanlike microtubule structure that helps separate chromosomes • Nuclear envelope breaks down • Chromosomes attached to fibers in spindle at the centromere

12. metaphase • Chromosomes line up in middle of cell

13. anaphase • Each sister chromatid separates and becomes an individual chromosome • Centromeres split • Chromosomes continue to move until they are in opposite poles

14. telophase • Chromosomes uncondense • Spindle breaks apart • Nuclear envelope reforms • Essentially, the opposite of prophase

15. cytokinesis • Separation of cytoplasm and its contents • In animal cells, membrane is squeezed in the middle until 2 cells are formed • Cleavage furrow • In plant cells, a cell plate will form • This will eventually become the cell wall

17. Uncontrolled cell growth • Cancer • Cancerous cells do not respond to signals that regulate growth of most cells • Divide uncontrollably  tumor • Cells can break lose and travel to other parts of body • Metastizing • Causes can be genetic or environmental • Effects depend on affected tissue

18. Chromosome number review • Humans have how many chromosomes? • 23 pairs of homologous chromosomes • We get half from mom and the other half from dad • 23 + 23 =46 • Diploid cell: contains 2 sets of chromosomes • Represented as 2n (n=number of chromosomes of organism) • Diploid cells contain 2 complete sets of genes

19. Chromosome number • Haploid cells: contain only a single set of genes • Represented as n (n= number of chromosomes) • Diploid number for humans? 2n=?... • 2n=46 • Haploid number in humans? N • If 2n=46, then n= • n=23

20. Haploid cells • Haploid cells are found in sexually reproducing organisms • Each parent offers on set of their own DNA (n) • Combination of gametes (sex cells) n + n = 2n • In humans: • Sperm (n) has 23 chromosomes • Egg (n) has 23 chromosomes • They combine to form a diploid zygote (2n)

21. Section 10-3 Meiosis • Meiosis: process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. • ***Very similar to mitosis only with an extra set of phases

22. Meiosis • Composed of two distinct divisions • Meiosis I • Meiosis II • Begins with a single diploid cell • Ends with 4 haploid cells

23. Homologous chromosomes • Homologous chromosomes: pairs of corresponding chromosomes from each parent • Ex. # 12 from mom matched up with # 12 from dad

24. Meiosis 1: • Prior: chromosomes replicated • Meiosis I: division of Homologous chromosomes • Results in 2 haploid daughter cells • Prophase I, Metaphase I, Anaphase I, Telophase I and cytokinesis

25. Prophase I: • Homologous chromosomes pair up (one from each parent) to form a tetrad(structure formed when homologues come together) • Crossingoveroccurs: results in the exchange of genetic information between homologouschromosomes • Produces new combinations of genes

26. Crossing over Occurs during Prophase I Overlapping arms of homologues have same information and can swap info at any point along their length *****increases genetic variation*****

27. Metaphase I Spindlefibers attach to centromere Tetrads (pair of homologouschromosomes) line up in middle of cell independent of each other

28. Anaphase I SpindleFibers pull homologouschromosomes toward opposite ends of the cell

29. Telophase I andCytokinesis Nuclear membranes reform Cell separates to become two cells *Cells produced have different genetic composition than the parent cell

30. Meiosis II • Meiosis II: paired chromatids divide • Each cell now has 2 chromatids • Almost exactly like mitosis!!

31. Prophase II Nothing really happens Chromosomes are already condensed and compacted Nuclear envelope goes away

32. Metaphase II Chromosomes line up similar to mitosis

33. Anaphase II Paired chromatids separated

34. Telophase II and cytokinesis Four haploid cells have been created

35. overview Meiosis I Meiosis II

36. Gamete formation Gamete: cell designed for sexual reproduction Example: sperm and egg Males make four sperm while females make one