Chapter 8 Cell Reproduction

1. Chapter 8 Cell Reproduction http://www.pisgahscience.com/bioonline/

2. Which of these pictures shows an organism with cell division taking place?

3. I. Introduction - Cell Division: • Occurs more often in young, growing organisms or when damaged tissue is repaired. • Some tissues like skin & intestinal cell grow throughout life while some- like nerve cells, do not divide again after full size achieved. • Genetic information must be divided between cells. • How does this happen?

4. Cell Division & Reproduction -allows for growth & reproduction of individuals -passes on genetic information to future generations.

5. In this chapter: • Chromosome Structure • Tightly coiled DNA molecules • Cell Division- • Mitosis (nuclear division) • Cytokinesis (division of cytoplasm) • Cell Reproduction- • Meiosis- Process reduces # of chromosomes to half of original cell to produce gametes.

6. II. Chromosome Structure • Chromosomes are rod-shaped structures made of DNA wrapped around a protein called HISTONE HISTONE PROTEIN DNA strand http://www.firedbydesign.com/1949/cell-animation/

7. Chromosome Structure When eukaryotic cells are ready to divide, the DNA coils tightly around proteins called HISTONES& forms CHROMOSOMES. • When a cell is NOT dividing, the DNA is loosely coiled in the cell NUCLEUS & is called CHROMATIN.

8. Chromosomes • Consist of 2 identical halves • Each half is called a CHROMATID. • Are attached to each other at the CENTROMERE. http://www.micro.utexas.edu/courses/levin/bio304/genetics/chromosome.gif

9. http://www.gla.ac.uk/cancerpathology/genemech/awest/chromatin.jpghttp://www.gla.ac.uk/cancerpathology/genemech/awest/chromatin.jpg

10. Chromosome Structure

11. How many Chromosomes in an Organism? • Look at this table- Does the # of chromosomes show how complex the organism is?..........NO!

12. B. Chromosome NumbersIn various species: • Adder’s Tongue Fern 1,262 • Carrot 18 • Cat 32 • Chimpanzee 48 • Human 46 • Dog 78 • Potato 48 • Earthworm 36 • Fruit fly 8 • Garden pea 20 • Lettuce 18 • Can different organisms can have same # chromosomes? …….. YES. • Can any conclusion about relatedness be made because of this? NO.

13. Sex chromosomes or Autosomes. • Sex Chromosomes (X, Y) - determine sex & carry genes for other characteristics. • Autosomes- all of the other chromosomes in an organism. • Example: Humans have 2 sex chromosomes & remaining 44 are autosomes. Humans have 46 chromosomes!

14. Sex chromosomes: • Females are XX • Males are XY • Males determine the sex of the baby- the sperm may contain either an X or a Y; eggs can only have Xs.

15. Homologous Chromosomes • Most organisms have 2 copies of each chromosome. • These pairs are called homologous chromosomes or “homologues”. geneticsmodules.duhs.duke.edu/Design/page.asp...

16. 2 copies of each gene • On each homologue- there are a genes for the same traits • For Example • if one of the homologous chromosomes has a gene for eye color, so will the other. http://course1.winona.edu/sberg/ILLUST/homolog1.gif

17. Homologous chromosomes • The 2 chromatids • are exact copies of each other- they’re identical. • attached by a centromere. • The Homologous chromosomes • ARE NOT exact copies. • (One set is from mom, one from dad) • They have genes for the same traits www.emunix.emich.edu The large red & blue chromosomes are homologous. The small purple & green chromosomes are homologous.

18. Copied from: www.stanford.edu/group/hopes/basics/dna/b5.html

19. Homologous chromosomes in humans www.ncbi.nlm.nih.gov/bookshelf/br.fcgi?book=g...

20. Karyotype • A picture (photomicrograph) of chromosomes. • Notice that humans have 46 chromosomes • 22 homologous pairs of autosomes • Plus 2 sex chromosomes.(Is this person male or female?) Karyotype Copied from: http://homepages.uel.ac.uk/V.K.Sieber/human.htm

21. A human karyotype

22. Diploid & Haploid cells • Diploid- cells having 2 sets of chromosomes. • Haploid- have only 1 set of chromosomes These are Sperm cells & Egg cells. **What is the number of chromosomes in a human haploid cell?(23)

23. Diploid is usually abbreviated 2n ( where “n” is the number of chromosomes in that organism) (in humans, the diploid- or 2n number is 46 • Haploid is 1n. • When an egg cell (1n) combines with a sperm cell (1n), the new cell will be diploid (2n) **What would happen if haploid cells were not used in sexual reproduction?

24. III. Cell Division • Prokaryotic Cell Division • Prokaryotes are bacteria that lack nuclei & membrane bound organelles. • Have a single circular stand of DNA • molecule is not coiled & do not form chromosomes. • Division is much simpler than in eukaryotic cells • Binary fission - how prokaryotic cells divide.

25. Binary fission: - Is the division of a prokaryotic cell into 2 identical offspring cells. (creates clones)

26. Cell Reproduction:Mitosis & Meiosis B. 2 kinds of cell division in eukaryotic cells: • Mitosisoccurs in cells for growth, development, repair or asexual reproduction. • Meiosisoccurs during formation of gametes for sexual reproduction www.ccs.k12.in.us/.../Humanembryology.htm

27. 2. The Cell Cycle • The cell cycle is the repeating set of events in the life of a cell. 2 main parts; further divided: • INTERPHASE – Time between cell divisions • G1 phase • S phase • G2 phase • CELL DIVISION- When chromosomes & cytoplasm are equally divided. • Mitosis - nuclear division • Cytokinesis - cytoplasm division

28. http://137.222.110.150/calnet/cellbio/page6.htm

29. 3 Stages of Interphase • G1 phase- cell grows to mature size. • “G1” stands for the time gap • after cell division & before DNA replication. • S phase- cell’s DNA is copied (synthesized). • (“S” stands for synthesize, meaning to “make”) • G2 phase- the cell prepares for cell division. • “G2” is the time gap between DNA synthesis & cell division. Some cells Exit the cell cycle: • Go phase-state where cells do not copy DNA or prepare for cell division. (example- CNS cells)

30. C. Mitosis -is division of thenucleus • results in: • two offspring cells • Diploid # chromosomes • genetically identical (clones) of the original cell.

31. Stages of Mitosis A process divided into 4 phases: 1. PROPHASE 2. METAPHASE 3. ANAPHASE • TELOPHASE Memory aids: "People Meet And Talk", or "PMAT" or “Pro met Anna (on the) telophone” or make up your own!

32. What happens during each phase of mitosis? • PROPHASE- - coilingof DNA into chromosomes. -The nucleus starts to disappear. -Centrosomes appear (In animal cells -centrioles appear also) & move to opposite poles of the cell. -Spindle fibers, made of microtubules, radiate from the centrosomes & forms the mitotic spindle & will be used to equally divide the chromosomes in the next phase.

33. 1. Prophase • Can you list some things that happen in prophase? • Find the structures in the drawing: • Nuclear membrane • Homologous Chromsomes • Chromatids • Centromere • Centrosomes • Spindle fibers; (look in book for 2 types of spindle fibers.) Drawings from: www.tqnyc.org

34. 2. METAPHASE • chromosomes are moved to the center of the cell • Note how they line up. • Chromosomes are easiest to ID under a microscope during metaphase -most karyotypes are made from cells in metaphase.

35. 3. ANAPHASE - the chromatids separate at the centromere & move to opposite poles. - after they separate, each chromatid is now considered to be a separate chromosome. (Tricky question- what “n” is a cell in anaphase? 4 )

36. 4. TELOPHASE After the chromosomes reach the opposite ends of the cell: • the spindle fibers disassemble, • the chromosomes return to a less tightly coiled state, • the nuclear envelope reforms in each newly forming cell.

37. http://jabberwiki.wikispaces.com/file/view/mitosis1.gif/53565174http://jabberwiki.wikispaces.com/file/view/mitosis1.gif/53565174

38. D. Cytokinesis • Division of the cytoplasm: • In animal cells- a cleavage furrowforms as the area of the cell membrane pinches the cell into 2. • In plant cells- a cell plateforms a new cell wall as vesicles from the golgi apparatus join together at the midline of the 2 dividing cells.

39. E. Control of Cell Division • A cell spends most of its time in interphase. • What triggers a cell to leave interphase & divide? • feedback from Checkpoints: • 1. Cell growth checkpoint (G1)- if the cell is healthy & grows to mature size, protiens will intiate DNA synthesis. • 2. DNA synthesis checkpoint (G2) proteins check results of DNA replication , signal OK • 3. Mitosis checkpoint, if ok- growth cycle starts.

40. Cell Division Errors • If mutations occur • proteins may not function properly • growth may not be controlled When control is lost = cancer.

41. IV. Meiosis • How it is different than mitosis: • reduces the number of chromosomes in new cells to half the number in the original cell. • Produces four haploid cells(gametes) • Different than two diploid cells as in mitosis.

42. Beginning meiosis: • Cells begin meiosis just like they begin mitosis, after interphase. • Cells must divide twice to reduce the number of chromosomes & so we have Meiosis I & Meiosis II. • Remember- the whole point of meiosis is to make gametes (which are 1N)

43. A. Meiosis- 8 phases • MEIOSIS I 1. PROPHASE I 2. METAPHASE I 3. ANAPHASE I 4. TELOPHASE I • MEIOSIS II 5. PROPHASE II 6. METAPHASE II 7. ANAPHASE II 8. TELOPHASE II

44. MEIOSIS I-what happens in each phase? • PROPHASE I -Spindle fibers appear & the nuclear membrane disappears as in mitosis. NOTE IN MEIOSIS I -HOMOLOGUES LINE UP NEXT TO EACH OTHER. -This pairing of homologous chromosomes, which does NOT occur in mitosis, is a synapsis. -Each pair of homologous chromosomes is a tetrad.

45. Genetic Recombination During synapsis, chromatids within a pair of homologues may twist around each other. Parts of the chromatids may break off & attach on the homologous chromosome. This is called crossing-over. Crossing over permits exchange of genetic materials = genetic recombination. • http://regentsprep.org/Regents/biology/units/evolution/crossovr.gif

46. Important to understand: • Crossing-over, • which is when portions of homologous chromosomes line up to form tetrads in synapsis. • exchange genetic material, • occurs during prophase I • results in genetic recombination.

47. 2. METAPHASE I • Pairs of homologous chromosomes (tetrads) line up on metaphase plate. 3. ANAPHASE I • Tetrads split- reducing the cells to haploid • The chromosomes have randomly separated- this is called Independent Assortment. 4. TELOPHASE I • 2 new cells begin to split off. Cytokinesis occurs.

49. MEIOSIS II Meiosis II occurs in both cells made in meiosis I 5. PROPHASE II- Chromosomes condense, nuclear membrane breaks down, spindle fibers form.  NOT preceded by replication or recombination. 6. METAPHASE II- Chromosomes line up on metaphase plate 7. ANAPHASE II- The chromosomes divide at the centromeres 8. TELOPHASE II- Chromosomes begin to uncoil, nuclear envelope reforms, followed by cytokinesis.

50. Stages of Meiosis, continued