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UWL BIO 203 - Life Cycles I
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BIO 203 1st Edition Lecture 14Outline of Last Lecture I. Cost of sexual reproductionII. Red-Queen hypothesis for the maintenance of sexIII. Advantages: Asexual vs. Sexual ReproductionIV. Disadvantages: Asexual vs. Sexual ReproductionV. Types of Asexual ReproductionVI. Sexual ReproductionOutline of Current Lecture I. Haploid vs. DiploidII. Mitosis vs. MeiosisIII. Cell division for Bacteria and ArchaeaIV. Unicellular EukaryotesV. Multicellular EukaryotesVI. Gametic Life CycleVII. Zygotic Life CycleVIII. Alternations of generationsIX. Mosses are gametophyte-dominantX. Ferns are sporophyte-dominantCurrent LectureI. Haploid vs. Diploida. Haploid means that the cell contains one set of chromosomesb. Diploid means that the cell contains two sets of chromosomesII. Mitosis vs. Meiosisa. Mitosis:i. One round of nuclear divisionii. Produces two identical daughter cellsiii. All replicated chromosomes line up independently at equator prior to divisioniv. Occurs in all stages of growth, development, and asexual reproduction; 1N and 2N cellsb. Meiosis:i. Two rounds of nuclear divisionii. Produces 4 non-identical 1N daughter cellsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.iii. Replicated chromosomes line up in homologous pairs at equator prior to divisioniv. Occurs only as part of sexual reproduction, and only to 2N cellsIII. Cell division for Bacteria and Archaeaa. Bacteria and Archaea reproduce through binary fissionb. Chromosome replication occursc. The two cells split apart from each otherIV. Unicellular Eukaryotesa. Commonly reproduce asexually, via mitosisb. Binary fission: Amoebozoa and Euglenids (major clade Excavata)c. Budding: a small progeny cell pinches off from a parent cell, seen in some Rhizaria (also unicellular fungi, aka yeasts!)d. Multiple fission: several nuclear divisions followed by cytokinesis (many individuals form at once); seen in Excavata, e.g. Trypanosoma and EuglenaV. Multicellular Eukaryotesa. Multicellular algae, plants, animals and fungi can all reproduce asexually using mitosisVI. Gametic Life Cyclea. Called a gametic life cycle because the products of meiosis aregametesb. Gametes are the only haploid cells in this life cyclec. Diploidphased. Meiosisto make haploidphase(gametes)e. Fertilization(to make diploidzygote)i. plasmogamy (fusion of cell membrane)ii. karyogamy (fusion of nuclei)f. Mitosisto make progeny diploidphaseg. Gametes are special haploid cells that can fuse together during fertilizationh. Produced prior to sexual mixingi. Diploid organisms produce gametes by meiosis, haploid organisms by mitosisj. Generally do not fuse with other gametes from the same organism or “mating type,” creating greater variabilityk. In most eukaryotes, gametes are morphologically identical to one anotherl. Other eukaryotes have independently evolved to have two types of gametesm. Small, motile gametes called “sperm,” produced by a “male”n. Large, immotile gametes called “eggs,” produced by a “female”o. Eggs store energy that can be used by the zygote after fertlizationp. Present in animals, of course, but also many others, e.g. plants!VII. Zygotic Life Cyclea. Called a zygotic life cycle because the zygote undergoes meiosis, returning the organism to a haploid conditionb. Zygotes are the only diploid cells in this life cyclec. Haploidphased. Mitosisto make haploid gametese. Fertilization(to make diploidzygote)i. plasmogamy (fusion of cell membranes)ii. karyogamy (fusion of nuclei)f. Meiosisto make progeny haploidphaseVIII. Alternations of Generationsa. The “C-ferns” and other land plants have this life cycleb. Alternation of generations because the haploid and diploid stages are both multicellular, and “take turns” = alternate with each otherc. Sporophytes (=SPTs) are 2n, make sporesd. Gametophytes (=GPTs) are 1n, make gametese. Haploidphasef. Mitosisto make haploid gametesg. Fertilization(to make diploidzygote)i. plasmogamy (fusion of cell membranes)ii. karyogamy (fusion of nuclei)h. Mitosisto make diploidphasei. Diploidphasej. Meiosisto make haploidsporesk. Mitosisto make progeny haploidphaseIX. Mosses are gametophyte-dominanta. Green, leafy mosses you know and love are 1N GPTsb. GPTs make gametes via mitosisc. Some individuals have antheridia to make spermd. Some GPT individuals make eggs in archegoniae. So sperm must get into the archegonium of another individual for fertilization to occurf. Either swim through the water (these plants live in wet environments)g. Or get carried by tiny arthropods!h. Fertilization produces a diploid zygotei. Zygote will divide through mitosis to develop into an immature sporophyte calledan embryoj. The embryo will develop into the sporophyte inside the archegonium of the female GPTk. Embryo grows through mitosis into a multicellular SPTl. Remains physically attached to GPTm. Makes 1N spores in sporangium at the top (also called a capsule)n. Sporangium dries out and spores disperse into the environmento. Spores germinate and grow into GPTs through mitosis, completing the cycle!X. Ferns are sporophyte-dominanta. But retain free-living


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