Common Characteristics Of Cells

observing anasynchronousculture.Mitosis - Karyokinesis and CytokinesisMitosis Timelines (Typical Vertebrate Cell)Pines, Jonathon and Conly L. Rieder. 2001. Re-staging mitosis: a contemporary viewof mitotic progression. Nature Cell Biology Vol g tab/ncb0101 e3 F2.html7

Evolution of MitosisMeiosis: Reduction Divisionc) Unicellular algae - diatomsFungia) Binary fission - bacteriab) Unicellular algae dinoflagellatesd) Most eukaryotesNote thechromosomeassortmentwhichcreatesdiversity –four kinds ofgametes.This happensin twodivisionsTwo greenchromosomesare from oneparent, twoblue from theother.The chromosomes are reduced from the diploid state (2 of eachchromosome, one from each parent) to the haploid state (one ofeach chromosome originating from either parent).Campbell et al., 1999Raven and Johnson, 1999Overview of -----------------II4 nucleiMeiosis INote thatProphase I isshown in fiveseparate steps.This is asignificant stagewhere veryimportantprocesses areoccurring. Notealso, that noreplication ofDNA occursbetween the firstand seconddivision.See Sadava et al., 2011, Fig. 11.17, p. 224-5.Beck et al., 1991Synapsis: A Most Important EventSynaptonemal Complexduring Prophase IRaven and Johnson, 1999Five Stages of Meiotic Prophase IFirstCondensationLeptotene (leptos fine )SecondPairingZygotene (zygon yolk,“Y”)ThirdRecombinationPachytene (pachus thick )FourthCoilingDiplotene (diplos double )FifthRecondensationDiakinesis (dia acrosskinesis movement )Solomon et al, 19998

Sequence of Events in Prophase ICrossing OverRaven and Johnson, 1999Meiosis IICell Cycles and DNA Copies Per CellBeck et al., 1991See Sadava et al., 2011, Fig. 11.17, p. 224-5.Comparison Between Mitosis and MeiosisNumber of copies of eachchromosome: Diploid is 2C – twocopies of each chromosome, onefrom each parent.Gametes are haploid,with only one copy ofeach chromosome.Beck et al., 1991Timing of Meiosis inVarious Life CyclesGametic Life Cycle Animals:Adult animals are diploid.Sporic Life Cycle Plants:Plants show an alternation ofgenerations with both diploidand haploid forms.Zygotic Life Cycle Fungi:Only the zygote is diploid andundergoes meiosis to formhaploid spores.Beck et al., 1991Beck et al., 1991See Sadava et al., 2011,Fig. 11.15, p. 222.9

Animal Life Cycles: GameticPlant Life Cycles: SporicGametophyte generation:n, haploid, shown inyellowBeck et al., 1991Beck et al., 1991Sporophyte generation:2n, diploid, shown inblueCampbell et al, 1999Asexual ReproductionFungi Life Cycles: ZygoticHydraBeck et al., 1991Filaments, called hyphae(mycelium), fuse to form aspecial type of filamentcalled a dikaryon twonuclei, but they are notjoined. Later the nucleifuse to form a zygote.Bacteria, E. coliRaven and Johnson, 1999Sexual ReproductionWouldn’t it be easier to just reproduce asexually? No annoyingmates! All of your genes would be passed on! Why not!Sexual Reproduction Sexual reproduction (sex) is the joining(fertilization or syngamy) of two haploidcells, called germ cells or gametes; one fromeach parent. Because half of an individual’s geneticinformation is lost in gamete production,there must be advantages of sexualreproduction. Gametes are distinguished from ordinary bodycells (called somatic cells that are diploid,or 2n) because they contain one rather thantwo of each chromosome (haploid, or n). If asexual reproduction is so simple andefficient, why is it not the universalmethod of reproduction?10

Why Are There So Many Sexual Species?Disadvantages Of Sexual ReproductionADVANTAGES from the fusion of sperm and egg. In meiosis there is a reshuffling of genetic materialthrough recombination. The fusion of a set ofchromosomes from each of two parents is a veryimportant evolutionary factor. Sexual reproduction increases genetic variability threeways:1. Independent assortment in meiosis2. Syngamy of male and female gamete3. Crossing-over in prophase I of meiosis Genetic recombination: a major consequence ofsexual reproduction is that it breaks upadapted gene complexes. Because of meiosis, half of an individual’sgenetic information is lost in gameteproduction. Sex has costs: Why produce male offspring whichmay require care and nurturing, when all theyprovide is sperm? Why look for mates?Sexual Reproduction And EvolutionParadoxically, the evolutionary process is bothrevolutionary and conservative Revolutionary in that the pace ofevolutionary change is quickened by theprocess of sexual reproduction, and Conservative in that this change may not befavored by selection and is eliminated.11

Cells are the fundamental unit of life (the basic unit of organization). All organisms are composed of cells. All cells come from preexisting cells. Common Characteristics Of Cells Cells must obtain and process energy Cells convert genetic in